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Hurricanes are powerful tropical cyclones with sustained wind speeds ranging from at least 74 mph (for category 1 storms) to more than 157 mph (for category 5 storms). Accurate prediction of the storm tracks is essential for hurricane preparedness and mitigation of storm impacts. In this paper, we cast the hurricane trajectory forecasting task as an online multi-lead time location prediction problem and present a framework called OMuLeT to improve path prediction by combining the 6-hourly and 12-hourly forecasts generated from an ensemble of dynamical (physical) hurricane models. OMuLeT employs an online learning with restart strategy to incrementally update the weights of the ensemble model combination as new observation data become available. It can also handle the varying dynamical models available for predicting the trajectories of different hurricanes. Experimental results using the Atlantic and Eastern Pacific hurricane data showed that OMuLeT significantly outperforms various baseline methods, including the official forecasts produced by the U.S. National Hurricane Center (NHC), by more than 10% in terms of its 48-hour lead time forecasts.

Eyewall replacement cycles (ERCs) are events that occur in intense tropical cyclones (TCs) and are difficult to predict. An ERC event involves a secondary outer eyewall that surrounds the inner eyewall. The outer eyewall slowly moves towards the eye and weakens the inner eyewall, eventually replacing the inner eyewall. During this process, wind speeds lower and the structure of a TC becomes disorganized, further weakening the storm. TCs often restrengthen after an ERC. Little is known about the process and as such, poses an obstacle to forecasters. The Automated Rotational Center Hurricane Eye Retrieval (ARCHER) Microwave-based Probability of Eyewall Replacement Cycle (MPERC) is an algorithm that uses 89-95 GHz passive microwave imagery and intensity estimates from the National Hurricane Center (NHC), Central Pacific Hurricane Center (CPHC), or the Joint Typhoon Warning Center (JTWC) to predict the possibility of an ERC. The effectiveness and ability of ARCHER MPERC was analyzed and compared to the NHC’s official reports on all Atlantic Basin tropical cyclones from 2017 to 2019. MPERC ultimately predicted seventeen ERCs in nine tropical cyclones. Of those, seven were valid ERCs. The algorithm works well, predicting approximately 41% of the total number of predictions correctly. However, MPERC did not predict five ERCs that were cited by the NHC. It was further found that it was true that MPERC produces incorrect results in sheared and dry environments.

The 2018 eastern North Pacific hurricane season featured well-above-average tropical cyclone activity. Of the 22 tropical storms that formed, 13 became hurricanes and nine reached major hurricane s...

The 2014 Northeast Pacific hurricane season was highly active, with above-average intensity and frequency events, and a rare landfalling Hawaiian hurricane. We show that the anomalous northern extent of sea surface temperatures and anomalous vertical extent of upper ocean heat content above 26 &deg, C throughout the Northeast and Central Pacific Ocean may have influenced three long-lived tropical cyclones in July and August. Using a variety of satellite-observed and -derived products, we assess genesis conditions, along-track intensity, and basin-wide anomalous upper ocean heat content during Hurricanes Genevieve, Iselle, and Julio. The anomalously northern surface position of the 26 &deg, C isotherm beyond 30&deg, N to the north and east of the Hawaiian Islands in 2014 created very high sea surface temperatures throughout much of the Central Pacific. Analysis of basin-wide mean conditions confirm higher-than-average storm activity during strong positive oceanic thermal anomalies. Positive anomalies of 15&ndash, 50 kJ cm&minus, 2 in the along-track upper ocean heat content for these three storms were observed during the intensification phase prior to peak intensity, advocating for greater understanding of the ocean thermal profile during tropical cyclone genesis and development.

The GOES-R Series observes the Atlantic and Eastern/Central Pacific hurricane basins and is able to continuously monitor tropical cyclones from cradle to grave. The hosted Advanced Baseline Imager (ABI) and Geostationary Lightning Mapper (GLM) instruments enable a variety of imagery and derived products with applications to tropical cyclone analysis. From the ABI, the frequent image refresh is useful for storm center-fixing and monitoring rapid convective evolution. The higher spatiotemporal sampling also enables better determination of storm eye characteristics. The expanded spectral bands allow for improved derived products such as sea surface temperatures (SSTs), atmospheric motion vectors (AMVs), split-window and red-green-blue (RGB)-type imagery to monitor the storm environment. GLM is a new capability from space and is enhancing the observation of lightning activity in hurricanes, which has been linked to intensity changes.

Tropical cyclone activity in the eastern North Pacific during 2017 was near the long-term average overall. Of the 18 tropical storms that formed, nine became hurricanes and four attained major hurr...

Properly organized data is vital for appropriate statistics and theories. In this study, it was hypothesized that raw tropical cyclone (TC) data labeled with the current Gregorian time system, dampened the dominant signals and order in the data. Therefore, the objective of this study was to explore and reorganize the data, using the TianGan-DiZhi (T-D) calendar. All 6 h TC records in 60 sidereal years over the western North Pacific (WNP) were investigated after the data were transferred from the Gregorian to T-D calendar. TianGan and DiZhi, two collections of elements in the T-D calendar, were then quantified to conduct correlation analyses with different TC parameters. The results showed significant temporal and spatial correlation between 6 h TC records and variables in the T-D calendar over different timescales. Temporally, 6 h TC records in the T-D summer, generally from May 5 to August 6, of the 60 sidereal years were significantly correlated with the strength difference between yearly TianGan and yearly DiZhi for the sidereal years. Spatially, the longitudes and latitudes of 6 h TC records were also significantly correlated with daily variables in the T-D calendar. We conclude that, TC data over the WNP can be better interpreted using the quantified T-D calendar than the Gregorian calendar. Since this ancient time-labeling tool can provide properly organized data, it might be used to modify some inputs in current numerical models to improve forecasting power. Key words: Tropical cyclone, frequency, temporal, sidereal, Gan-Zhi, calendar.

A novel approach in retrieving hurricane maximum winds using simulated NASA Cyclone Navigation Satellite System (CYGNSS) data is presented. Five hundred fifty two hurricane wind fields, from the 2010–2011 Atlantic and Eastern pacific hurricane seasons, were used to test the algorithm. These wind fields have been obtained from the hurricane weather research and forecasting model (HWRF). Power-versus-delay waveforms associated with specular points located along CYGNSS tracks crossing these wind fields were simulated. These “storm” power-versus-delay waveforms were compared to “reference” power-versus-delay waveforms generated over a set of synthetic Willoughby storms with known maximum wind speeds. The retrieved maximum wind speeds are compared against the hurricane research division reanalysis data (Best Track) and HWRF. For Best Track maximum wind speeds less than 40 m/s and greater than 40 m/s, the overall bias against Best Track is 11.3 and 2.1 m/s, respectively. When comparing against HWRF maximum wind speeds less than 40 m/s and greater than 40 m/s, the overall bias is 11.5 and 3.0 m/s, respectively. These results are improved when translation effects were applied to these synthetic storms: compared against Best Track for maximum wind speeds less than 40 m/s and greater than 40 m/s, the biases are 9.0 and $-$ 1.13 m/s, respectively. When compared against HWRF, the biases are 8.6 and 0.4 m/s, respectively.

Hurricane Patricia in 2015 was the strongest Pacific hurricane to make landfall in Mexico. Although Patricia fortuitously spared major cities, it reminded us of the threat tropical cyclones (TCs) pose in the eastern North Pacific (ENP) and the importance of improving our understanding and prediction of ENP TCs. Patricia’s intensity and the active 2015 ENP hurricane season have been partially attributed to the strong El Niño in 2015, however there is still a lack of fundamental understanding of the relationship between El Niño-Southern Oscillation (ENSO) and ENP TCs. Here, we demonstrate that ENSO drives intrabasin variability of ENP TCs, with enhanced (reduced) TC frequency in the western portion of the ENP during El Niño (La Niña), but reduced (enhanced) TC frequency in the eastern nearshore area, where landfalling TCs preferentially form. This intrabasin difference is primarily driven by the Central American Gap Winds (CAGW), which intensify (weaken) during El Niño (La Niña), producing low-level anticyclonic (cyclonic) relative vorticity anomalies and thus an unfavorable (favorable) environment for TC genesis. These findings shed new light on the dynamics linking ENP TC activity to ENSO, and highlight the importance of improving CAGW representation in models to make skillful seasonal forecasts of ENP TCs.

This study uses observations and model reanalyses to examine the multiscale processes associated with four high-impact extreme weather events (EWEs) over North America during late October 2007. The EWEs consisted of wind-driven wildfires in California, prolonged anomalous cold conditions in Mexico linked to two cold surges, heavy rainfall in the eastern United States, and severe flood-producing heavy rainfall in southern Mexico. The EWEs involved a pronounced large-scale flow reconfiguration across the North Pacific and North America in conjunction with the formation of a high-amplitude Rossby wave train. The flow reconfiguration involved perturbations to the North Pacific jet stream linked to polar, midlatitude, and tropical disturbances, including three tropopause-level polar disturbances originating over northeastern Asia, transient extratropical cyclones, a diabatic Rossby vortex, and western North Pacific Tropical Cyclone Kajiki. Eulerian and Lagrangian diagnostics indicate that ridge amplification within the wave train was enhanced in connection with latent heat release along warm conveyor belts rooted in the tropics and subtropics over the North Pacific. Two anticyclonic Rossby wave breaking events over North America established synoptic-scale conditions that supported the EWEs. The results highlight how the large- and synoptic-scale flow can evolve to facilitate multiple geographically separated but dynamically linked EWEs. Based on the results, it is posited that during autumn the North Pacific jet stream may be particularly conducive to large-scale flow amplification, possibly resulting in EWEs, in response to perturbations associated with tropical, midlatitude, and polar disturbances.

In recent years, a number of extremely powerful tropical cyclones have revived community debate on methodologies used to estimate the lifetime maximum intensity (LMI) of these events. And how do these storms rank historically? In this study, the most updated version of an objective satellite-based intensity estimation algorithm [advanced Dvorak technique (ADT)] is employed and applied to the highest-resolution (spatial and temporal) geostationary satellite data available for extreme-intensity tropical cyclones that occurred during the era of these satellites (1979–present). Cases with reconnaissance aircraft observations are examined and used to calibrate the ADT at extreme intensities. Bias corrections for observing properties such as satellite viewing angle and image spatiotemporal resolution, and storm characteristics such as small eye size are also considered. The results of these intensity estimates (maximum sustained 1-min wind) show that eastern North Pacific Hurricane Patricia (2015) ranks as the strongest storm in any basin (182 kt), followed by western North Pacific Typhoons Haiyan (2013), Tip (1979), and Gay (1992). The following are the strongest classifications in other basins—Atlantic: Gilbert (1988), north Indian Ocean basin: Paradip (1999), south Indian Ocean: Gafilo (2004), Australian region: Monica (2006), and southeast Pacific basin: Pam (2015). In addition, ADT LMI estimates for four storms exceed the maximum allowable limit imposed by the operational Dvorak technique. This upper bound on intensity may be an unnatural constraint, especially if tropical cyclones get stronger in a warmer biosphere as some theorize. This argues for the need of an extension to the Dvorak scale to allow higher intensity estimates.

A statistical model of northeastern Pacific Ocean tropical cyclones (TCs) is developed and used to estimate hurricane landfall rates along the coast of Mexico. Mean annual landfall rates for 1971–2014 are compared with mean rates for the extremely high northeastern Pacific sea surface temperature (SST) of 2015. Over the full coast, the mean rate and 5%–95% uncertainty range (in parentheses) for TCs that are category 1 and higher on the Saffir–Simpson scale (C1+ TCs) are 1.24 (1.05, 1.33) yr−1 for 1971–2014 and 1.69 (0.89, 2.08) yr−1 for 2015—a difference that is not significant. The increase for the most intense landfalls (category-5 TCs) is significant: 0.009 (0.006, 0.011) yr−1 for 1971–2014 and 0.031 (0.016, 0.036) yr−1 for 2015. The SST impact on the rate of category-5 TC landfalls is largest on the northern Mexican coast. The increased landfall rates for category-5 TCs are consistent with independent analysis showing that SST has its greatest impact on the formation rates of the most intense northeastern Pacific TCs. Landfall rates on Hawaii [0.033 (0.019, 0.045) yr−1 for C1+ TCs and 0.010 (0.005, 0.016) yr−1 for C3+ TCs for 1971–2014] show increases in the best estimates for 2015 conditions, but the changes are statistically insignificant.

The 2015 hurricane season in the eastern and central Pacific Ocean (EPO and CPO), particularly around Hawaii, was extremely active, including a record number of tropical cyclones (TCs) and the first instance of three simultaneous category-4 hurricanes in the EPO and CPO. A strong El Niño developed during the 2015 boreal summer season and was attributed by some to be the cause of the extreme number of TCs. However, according to a suite of targeted high-resolution model experiments, the extreme 2015 EPO and CPO hurricane season was not primarily induced by the 2015 El Niño tropical Pacific warming, but by warming in the subtropical Pacific Ocean. This warming is not typical of El Niño, but rather of the Pacific meridional mode (PMM) superimposed on long-term anthropogenic warming. Although the likelihood of such an extreme year depends on the phase of natural variability, the coupled GCM projects an increase in the frequency of such extremely active TC years over the next few decades for EPO, CPO, and Hawaii as a result of enhanced subtropical Pacific warming from anthropogenic greenhouse gas forcing.

Tropical cyclone (TC) climatological characteristics with passage from the Western North Pacific (WNP) into the South China Sea (SCS) during the June - November season are analyzed in this study. These TCs tend to form in the WNP west of 150°E, and on average westward by 7 - 12° in longitude than TCs that do not track into the SCS. Their formation locations migrate with the monsoon trough, moving northward from June to August, and southward from September to November. The probability of a WNP TC moving into the SCS varies seasonally, with only 12 - 18% of the WNP TCs doing so during August-September due to more northern TC formation. However, this probability rises to 25 - 26% in June - July and 25 - 32% in October - November with more southern TC formation. The passage-type TCs generally form in the eastern part of an elongated lower-level cyclonic anomaly of the 10-day low-pass filtered environmental circulation in the 10 - 20°N zone, which is paired with an anticyclonic anomaly to the north. Between this circulation pair, anomalous easterly flows steer these TCs westward, giving them a westward track into the SCS. The formation of these passage-type TCs is associated with a southward displacement of the monsoon trough and a westward intensification of the Pacific subtropical high in August and September. During June - July (October - November), the associated features appear as a southeastward (meridional) expansion of the monsoon trough and a northward displacement of the Pacific subtropical high.

In this study, the design of movable multilevel nesting (MMLN) in the Hurricane Weather Research and Forecasting (HWRF) modeling system is documented. The configuration of a new experimental HWRF system with a much larger horizontal outer domain and multiple sets of MMLN, referred to as the “basin scale” HWRF, is also described. The performance of this new system is applied for various difficult forecast scenarios such as 1) simulating multiple storms [i.e., Hurricanes Earl (2010), Danielle (2010), and Frank (2010)] and 2) forecasting tropical cyclone (TC) to extratropical cyclone transitions, specifically Hurricane Sandy (2012). Verification of track forecasts for the 2011–14 Atlantic and eastern Pacific hurricane seasons demonstrates that the basin-scale HWRF produces similar overall results to the 2014 operational HWRF, the best operational HWRF at the same resolution. In the Atlantic, intensity forecasts for the basin-scale HWRF were notably worse than for the 2014 operational HWRF, but this deficiency was shown to be from poor intensity forecasts for Hurricane Leslie (2012) associated with the lack of ocean coupling in the basin-scale HWRF. With Leslie removed, the intensity forecast errors were equivalent. The basin-scale HWRF is capable of predicting multiple TCs simultaneously, allowing more realistic storm-to-storm interactions. Even though the basin-scale HWRF produced results only comparable to the regular operational HWRF at this stage, this configuration paves a promising pathway toward operations.

Recent studies have highlighted the role of subsurface ocean dynamics in modulating eastern Pacific (EPac) hurricane activity on interannual time scales. In particular, the well-known El Niño–Southern Oscillation (ENSO) recharge–discharge mechanism has been suggested to provide a good understanding of the year-to-year variability of hurricane activity in this region. This paper investigates the influence of equatorial subsurface subannual and intraseasonal oceanic variability on tropical cyclone (TC) activity in the EPac. That is to say, it examines previously unexplored time scales, shorter than interannual, in an attempt to explain the variability not related to ENSO. Using ocean reanalysis products and TC best-track archive, the role of subannual and intraseasonal equatorial Kelvin waves (EKW) in modulating hurricane intensity in the EPac is examined. It is shown first that these planetary waves have a clear control on the subannual and intraseasonal variability of thermocline depth in the EPac cyclone-active region. This is found to affect ocean subsurface temperature, which in turn fuels hurricane intensification with a marked seasonal-phase locking. This mechanism of TC fueling, which explains up to 30% of the variability of TC activity unrelated to ENSO (around 15%–20% of the total variability), is embedded in the large-scale equatorial dynamics and therefore offers some predictability with lead time up to 3–4 months at seasonal and subseasonal time scales.

The presence of a near-record El Nino and a positive Pacific Meridional Mode provided an extraordinarily warm background state that fueled the 2015 eastern North Pacific hurricane season to near-record levels. We find that the western portion of the eastern North Pacific, referred to as the Western Development Region (WDR; 10°–20°N, 116°W–180°), set records for named storms, hurricane days, and Accumulated Cyclone Energy in 2015. When analyzing large-scale environmental conditions, we show that record warm sea surface temperatures, high midlevel relative humidity, high low-level relative vorticity, and record low vertical wind shear were among the environmental forcing factors contributing to the observed tropical cyclone activity. We assess how intraseasonal atmospheric variability may have contributed to active and inactive periods observed during the 2015 hurricane season. We document that, historically, active seasons are associated with May–June El Nino conditions, potentially allowing for predictability of future active WDR seasons.

Sea surface temperature (SST) of the eastern equatorial Pacific is a key component of tropical oceanic and atmospheric circulation with global teleconnections. Forcing factors such as local and high-latitude insolation changes, ice sheet size and albedo feedbacks, and greenhouse gas radiation have been proposed as controls of long-term eastern tropical Pacific SST, though the precise role each mechanism plays is not fully known on glacial-interglacial or longer timescales. Here proposed mechanisms are evaluated by comparing orbital-scale records of eastern Pacific SST with forcing variability over the past 1.5 Ma. The primary SST records are a compilation of new and existing data from Ocean Drilling Program Site 1239 at the northeastern margin of the modern eastern Pacific cold tongue and Site 846 SST within the cold tongue. Using time series analysis, we test previously proposed mechanisms for control of long-term tropical SST change and SST gradients in the eastern Pacific. We find that within statistical uncertainties, in the precession band eastern Pacific SST is consistent with direct forcing by equatorial radiation changes in the tropical cold season (summer-fall) rather than inversely correlated as previously suggested. In the obliquity band high-latitude solar forcing leads or is in phase with eastern equatorial Pacific SST, while in the eccentricity band atmospheric greenhouse gas concentrations are closely associated with cold tongue SST. Pleistocene eastern Pacific SST gradients indicate that the gradient on the northern margin of the cold tongue strengthened through the mid-Pleistocene transition, a result compatible with the cold tongue becoming more focused at ~900–650 ka.

During the second half of 2014, the tropical Pacific was in a state marginally consistent with El Nino. While oceanic indicators were indicative of a weak El Nino event, a number of atmospheric indicators were not, and a number of forecast centers did not declare an El Nino. Nonetheless, the most active tropical cyclone basins of the northern hemisphere—those of the North Atlantic and Pacific—showed tropical cyclone statistics that in some respects were consistent with El Nino. In particular, the numbers of relatively intense storms in the four basins considered—major hurricanes in the Eastern North Pacific and North Atlantic, super typhoons in the Western North Pacific, and hurricanes in the Central North Pacific—formed a pattern strongly consistent with El Nino.

The 2015 eastern North Pacific hurricane season was very active. Of the 18 cyclones that reached tropical storm strength, 13 became hurricanes and nine reached major hurricane status (category 3 or...

In early November 2006, an unnamed tropical cyclone (TC) formed via the tropical transition (TT) process at 42°N over the eastern North Pacific. An extratropical cyclone (EC), developing downstream of a thinning upper-tropospheric trough over the eastern North Pacific, served as the precursor disturbance that would ultimately undergo TT. The TT of the unnamed TC was extremely unusual—occurring over ~16°C sea surface temperatures in a portion of the eastern North Pacific basin historically devoid of TC activity. This paper 1) identifies the upper- and lower-tropospheric features linked to the formation of the EC that transitions into the unnamed TC, 2) provides a synoptic overview of the features and processes associated with the unnamed TC’s TT, and 3) discusses the landfall of the weakening cyclone along the west coast of North America. As observed in previous studies of TT, the precursor EC progresses through the life cycle of a marine extratropical frontal cyclone, developing a bent-back warm front on its northern and western sides and undergoing a warm seclusion process. Backward air parcel trajectories suggest that air parcels isolated in the center of the transitioning cyclone were warmed in the lower troposphere via sensible heating from the underlying sea surface. Vertical cross sections taken through the center of the cyclone during its life cycle reveal its transformation from an asymmetric, cold-core, EC into an axisymmetric, warm-core, TC during TT. Ensemble reforecasts initialized after TT highlight the relatively low forecast skill associated with the landfall of the weakening cyclone.

This study examines future projections of sea level pressure change in the North Pacific and its impact on winter precipitation changes in California. The multimodel analysis, based on the Coupled Model Intercomparison Project phase 5 models under the Representative Concentration Pathway 8.5 scenario, shows a robust sea level pressure change in the late 21st century over the western North Pacific in which both the Aleutian Low and the North Pacific subtropical high (NPSH) shift poleward in concert with a widening of the Hadley cell. This change is partly explained by a systematic increase of static stability in the subtropics. Despite its robustness, the projected NPSH changes over the eastern North Pacific exhibit a substantial intermodel spread, contributing as a cause for uncertain projections of precipitation changes in California. This intermodel spread in the eastern North Pacific is associated with a Pacific Decadal Oscillation-like surface temperature change in the western North Pacific and the resulting meridional temperature gradient change. This study points to a major source of uncertainty for the response of winter precipitation to global warming over the West Coast of North America: atmosphere-ocean coupling in the North Pacific.

The 2010 Atlantic hurricane season was marked by above-average tropical cyclone activity with the formation of 19 tropical storms. A total of 12 of the storms became hurricanes and 5 became major hurricanes (category 3 or higher on the Saffir–Simpson hurricane wind scale). In addition, there were two tropical depressions that did not reach storm strength. These totals were well above the long-term averages of 11 named storms, 6 hurricanes, and 2 major hurricanes. The areas most affected by the 2010 storms were eastern Mexico, Central America, and the island nations of the western Caribbean Sea, where multiple strikes occurred. In addition, two hurricanes struck eastern Canada. Despite the high level of activity, no hurricanes made landfall in the United States in 2010. The death toll from the 2010 Atlantic tropical cyclones was 189. A verification of National Hurricane Center official forecasts during 2010 is also presented. The 2010 mean track errors were slightly larger than the previous 5-yr average at 12 and 24 h and much smaller at the other forecast times, even though the 2010 track forecasts were more difficult than normal. The 2010 mean intensity forecast errors were larger than the previous 5-yr average at 12–48 h, smaller at the longer forecast times, and had a high bias at all forecast times. As with the track forecasts, the 2010 intensity forecasts were more difficult than normal at all forecast times.

The NOAA Gulfstream IV (G-IV) routinely deploys global positioning system dropwindsondes (GPS sondes) to sample the environment around hurricanes that threaten landfall in the United States and neighboring countries. Part of this G-IV synoptic surveillance flight pattern is a circumnavigation 300–350 km from the circulation center of the hurricane. Here, the GPS sondes deployed over two consecutive days around Hurricane Felicia (2009) as it approached Hawaii are examined. The circumnavigations captured only the final stages of decay of the once-category-4 hurricane. Satellite images revealed a rapid collapse of the deep convection in the eyewall region and the appearance of the low-level circulation center over ~8 h. Midlevel dry air associated with the Pacific high was present along portions of the circumnavigation but did not reach the eyewall region during the period of rapid dissipation of the deep clouds. In contrast, the subtropical jet stream (STJ) enhanced the deep-layer vertical shear of the horizontal wind (VWS; 850–200 hPa) to greater than 30 m s−1 first in the northwest quadrant; ~6 h later the STJ was estimated to reach the eyewall region of the hurricane and was nearly coincident with the dissipation of deep convection in the core of Felicia. Felicia’s demise is an example of the STJ enhancing the VWS and inhibiting intense hurricanes from making landfall in Hawaii. The authors speculate that VWS calculated over quadrants rather than entire annuli around a hurricane may be more appropriate for forecasting intensity change.

The Hurricane Weather Research and Forecasting Model (HWRF) was operationally implemented with a 27-km outer domain and a 9-km moving nest in 2007 (H007) as a tropical cyclone forecast model for the North Atlantic and eastern Pacific hurricane basins. During the 2012 hurricane season, a modified version of HWRF (H212), which increased horizontal resolution by adding a third (3 km) nest within the 9-km nest, replaced H007. H212 thus became the first operational model running at convection-permitting resolution. In addition, there were modifications to the initialization, model physics, tracking algorithm, etc. This paper compares H212 hindcast forecasts for the 2010–11 Atlantic hurricane seasons with forecasts from H007 and H3GP, a triply nested research version of HWRF. H212 reduced track forecast errors for almost all forecast times versus H007 and H3GP. H3GP was superior for intensity forecasts, although H212 showed some improvement over H007. Stratifying the cases by initial vertical wind shear revealed that the main weakness for H212 intensity forecasts was for cases with initially high shear. In these cases, H212 over- and under-intensified storms that were initially stronger and weaker, respectively. These results suggest the primary deficiency negatively impacting H212 intensity forecasts, especially in cases of rapid intensification, was that physics calls were too infrequent for the 3-km inner mesh. Correcting this deficiency along with additional modifications in the 2013 operational version yielded improved track and intensity forecasts. These intensity forecasts were comparable to statistical–dynamical models, showing that dynamical models can contribute to a decrease in operational forecast errors.

Tropical cyclone activity during the 2014 eastern North Pacific hurricane season was well above normal, and by several measures was the highest since the early 1990s. Of the 20 tropical storms that...

"Using data from closely spaced CTD profiles and satellite imagery we investigated the effect of hurricane Rick on the sea surface temperature (SST) and the upper mixed layer of the southwestern Mexican Pacific coast. Effects of ENSO 1997 - 1998 in this regio n are also discussed by analysing SST maps. Coincident hydrographic measurements were carried out during an oceanographic campaign over the area in November 1997. Results revealed an increment of SST between 3 to 4°C above the climatological mean temperatu re (25° ± 2°C), in the Mexican Tropical Pacific, during ENSO. I n situ measurements show instabilities in the upper mixed layer after the pass of the hurricane in oceanic areas. Satellite and historical databases enabled interpretation and analyses of ENSO’ s effect on the southwest coast of Mexico."

Category 4 Hurricane Kenneth (HK) experienced unpredicted rapid weakening when it stalled over a cold core eddy (CCE) on 19–20 September 2005, 2800 km SE of Hawaii. Maximum sea surface temperature (SST) cooling of 8–9°C and a minimum aerially averaged SST of 18.3°C (over 8750 km2) characterized its cool wake. A 3-D mixed-layer model enabled estimation of enthalpy fluxes (latent and sensible heat), as well as the relative importance of slow translation speed (Uh) compared with the preexisting CCE. As Uh dropped below 1.5 m s−1, enthalpy fluxes became negative, cutting off direct ocean energy flux to HK. Although HK's weakening was attributed to wind shear, our results indicate that slow Uh and consequent intense SST cooling were the main causes. The tropical cyclone-intensified CCE experienced rapid growth in magnitude (−6 to −40 cm), increased diameter (60 to 350 km), elevated chlorophyll a for 4 months, and 12 month longevity.

Recent improvements in the theoretical understanding of the relationship between tropical cyclones (TCs) and their large-scale environments have resulted in significant improvements in the skill for forecasting TC activity at daily and seasonal time-scales. However, future changes in TC activity under a warmer climate remain uncertain, particularly in terms of TC genesis locations and subsequent pathways. Applying a track-pattern-based statistical model to 22 Coupled Model Intercomparison Project Phase 5 (CMIP5) model runs for the historical period and the future period corresponding to the Representative Concentration Pathway 8.5 emissions scenarios, this study shows that in future climate conditions, TC passage frequency will decrease over the North Atlantic, particularly in the Gulf of Mexico, but will increase over the western North Pacific, especially that hits Korea and Japan. Unlike previous studies based on fine-resolution models, an ensemble mean of CMIP5 models projects an increase in TC activity in the western North Pacific, which is owing to enhanced subtropical deep convection and favorable dynamic conditions therein in conjunction with the expansion of the tropics and vice versa for the North Atlantic. Our results suggest that North America will experience less TC landfalls, while northeast Asia will experience more TCs than in the present-day climate.

Although a significant relationship between near-time sea surface temperature (SST) and tropical cyclone (TC) intensity has been found for many major TC basins, this topic has not been explored in the eastern North Pacific (ENP) basin. When the main development region of the (ENP) Ocean is subdivided into eastern (EDR) and western (WDR) development regions, SSTs show a weak, yet significant, positive relationship with intensities of the six-hourly TC observations and storms’ maximum strengths only in the WDR. This SST-storm intensity relationship is most apparent for the maximum lifetime TC intensity of WDR major hurricanes. The maximum strength of major hurricanes in the ENP basin is more clearly established in the WDR where SST is at least 25 °C, well below the minimum SST value that is observed in the North Atlantic basin.

US coastal cities are regularly subjected to destruction by tropical cyclones. The risk of tropical cyclone winds varies along the length of the coastline. We analyze landfalling North Atlantic basin tropical cyclones whose intensities are considered extreme relative to their landfall location. To be considered extreme, a tropical cyclone’s wind speed must exceed the 50-year return level for a given city. Of interest is the spatial and temporal patterns of these extreme hurricane wind events for fifteen coastal cities, which are organized into four coastal regions: Northeast Atlantic, Southeast Atlantic, Florida, and Gulf. Findings suggest that extreme hurricanes along the Florida and Atlantic coasts cluster in time, specifically decades, while there is no temporal clustering detected along the Gulf. Atlantic coast hurricane clusters are in part due to the likelihood of one intense hurricane impacting multiple coastal cities, which is unlikely to happen along the Gulf due to the alignment of the coast. It is also unlikely for an intense hurricane to impact multiple Florida cities as an extreme hurricane, suggesting a physical mechanism enables the temporal clustering seen here. The results of this work advocate for annual and decadal hurricane risk to include: (1) the likelihood of temporal clusters of extreme hurricanes along the Atlantic and Florida coasts and (2) extreme hurricanes impacting multiple cities along the Atlantic coast.

Deciphering how the climate system has controlled North Atlantic tropical cyclone activity through the Holocene will require a larger observational network of prehistoric hurricane activity. Problematically, the tropical North Atlantic is dominated by carbonate landscapes that typically preserve poorer quality coastal sediment records in comparison to their temperate-region counterparts (e.g., sedimentation continuity and rate). Coastal karst basins (CKBs), such as sinkholes, blueholes, and underwater caves, are widely distributed on carbonate platforms and contain overlooked sedimentary records. Here we present a millennium of hurricane deposits on the Little Bahama Bank archived in a 165 cm core that was extracted from 69 m below sea level in a bluehole on Great Abaco Island, The Bahamas. The coarse-grained overwash deposits associated with both hurricanes Jeanne (2004) and Floyd (1999) were identified using radioisotopes (137Cs, 14C, 210Pb), and indicate that the bluehole is sensitive to hurricane-induced sedimentation. Over the last millennium, the Little Bahama Bank experienced heightened hurricane activity from 1350 to 1650 AD. The simplest explanation for this active interval is that favorable climate conditions (El Nino, West African Monsoon, and sea surface temperatures) encouraged North Atlantic hurricane activity at that time. However, asynchronous hurricane activity at similar latitudes in the North Atlantic and Gulf of Mexico suggest that regional oceanography has modulated or amplified regional hurricane activity over the last millennium.

A reanalysis of the Atlantic basin tropical storm and hurricane database (“best track”) for the period from 1931 to 1943 has been completed as part of the Atlantic Hurricane Database Reanalysis Project. This reassessment of the main archive for tropical cyclones of the North Atlantic Ocean, Caribbean Sea, and Gulf of Mexico was necessary to correct systematic biases and random errors in the data as well as to search for previously unrecognized systems. Methodology for the reanalysis process for revising the track and intensity of tropical cyclone data is largely unchanged from that of the preceding couple of decades and has been detailed in a previous paper on the reanalysis. Accurate Environmental Forecasting’s numerical weather prediction-based wind field model was utilized here to help determine which states were impacted by various hurricane force winds in several U.S. landfalling major hurricanes during this era. The 1931–43 dataset now includes 23 new tropical cyclones, excludes five systems previously considered tropical storms, makes generally large alterations in the intensity estimates of most tropical cyclones (at various times both toward stronger and weaker intensities), and typically adjusts existing tracks with minor corrections. Average errors in intensity and track values are estimated for both open ocean conditions as well as for landfalling systems. Finally, highlights are given for changes to the more significant hurricanes to impact the United States, Central America, and the Caribbean for this time period.

A 42-yr study of eastern North Pacific tropical cyclones (TCs) undergoing extratropical transition (ET) is presented using the Japanese 55-yr Reanalysis dataset. By using cyclone phase space (CPS) to differentiate those TCs that undergo ET from those that do not, it is found that only 9% of eastern North Pacific TCs that developed from 1971 to 2012 complete ET, compared with 40% in the North Atlantic. Using a combination of CPS, empirical orthogonal function (EOF) analysis, and composite analysis, it is found that the evolution of ET in this basin differs from that observed in the North Atlantic and western North Pacific, possibly as a result of the rapidly decreasing sea surface temperatures north of the main genesis region. The presence of a strong, deep subtropical ridge extending westward from North America into the eastern North Pacific is a major factor inhibiting ET in this basin. Similar to other basins, eastern North Pacific ET generally occurs in conjunction with an approaching midlatitude trough, which helps to weaken the ridge and allow northward passage of the TC. The frequency of ET appears to increase during developing El Niño events but is not significantly affected by the Pacific decadal oscillation.

Hurricanes annually threaten the Atlantic Ocean margins. Historical hurricane records are relatively short and palaeohurricane sedimentary archives provide a geological and climatic context that sheds light on future hurricane activity. Here we review palaeo-trends in hurricane activity elucidated from sedimentary archives. We discuss dating methods, site selection and stat- istics associated with previously published records. These archives have been useful for under- standing the long-term evolution of coastal systems and the response of intense hurricane activity to climatic changes. Regional shifts in hurricane overwash on centennial to millennial timescales have been linked to various climatic modes of variability, including El Nino/Southern Oscillation and the North Atlantic Oscillation, but could also reflect regional-scale controls on hurricane activity.

In the Western Hemisphere, tropical storms or hurricanes form in the North Atlantic and eastern North Pacific. Previous studies have focused on storm variability in the frequency, duration, and intensity in each basin. Here we find that the tropical storm genesis location in one ocean basin ties to the other one. On both interannual and multidecadal timescales, a northward (southward) shift of the tropical storm genesis location is associated with a southward (northward) variation in the other ocean basin. The change of cross-Central America wind in the upper troposphere, which induces an out-of-phase relation of vertical wind shear, bridges storm activity in the two ocean basins. Sea surface temperatures in both the tropical Pacific and North Atlantic can induce the zonal wind change across Central America. It implies that hurricane outlooks can be improved by considering the two ocean basins together, and thus helping reduce the damage caused by hurricane landfall.

The Western North Pacific (WNP) is the most favorable area in the world for the generation of tropical cyclones (TCs). As the most intense weather system, TCs play an important role in the change of ocean environment in the WNP. Based on many investigations published in the literature, we obtained a collective and systematic understanding of the influence of TCs on ocean components in the WNP, including sea temperature, ocean currents, mesoscale eddies, storm surges, phytoplankton (indicated by chlorophyll a). Some ocean responses to TCs are unique in the WNP because of the existence of the Kuroshio and special geographical configurations such as the South China Sea.

A spatial analysis of intensity change has yet to be considered in hurricane climatology. Here we use a unique hourly interpolated version of the Atlantic hurricane dataset together with a novel spatial tessellation of the basin to examine the climatology of hurricane intensity change. We find that the frequency of hurricanes is highest across the central part of the basin, but regions of highest intensity are located farther south across the Caribbean. Standard errors of the mean intensities are largest in the regions adjacent to land. Highest mean intensification rates are found in the Gulf of Mexico and the Caribbean Sea, and the mean intensification is getting larger in the southeast portion of the basin. We find greater spatial coherency in intensification rates over the period from 1986 to 2011 compared with the period from 1967 to 1985. The reason for this change is unknown but it is likely due to improved surveillance technology. We also find that the statistical relationship between intensity and intensification is getting stronger and tighter and note that this might be associated with the implementation of the Dvorak Technique.

We lack an understanding of the geographic and temporal controls on South Pacific cyclone activity. Overwash records from backbarrier salt marshes and coastal ponds have been used to reconstruct tropical cyclone strikes in the North Atlantic basin. However, these specific backbarrier environments are scarce in the South Pacific, with cyclone records limited primarily to the period of modern observation. This instrumental record suggests a correlation with the El Nino–Southern Oscillation (ENSO), but longer records are necessary to test this relationship over geologic timescales and explore other potential climate drivers of tropical cyclone variability. Deep lagoons behind coral reefs are widespread in the Pacific and provide an alternative setting for developing long-term sedimentary reconstructions of tropical cyclone occurrence. Coarse-grained event deposits within the sediments of a back-reef lagoon surrounding Tahaa reveal a 5000-year record of cyclone occurrences. Timing of recent high-energy deposits matches well with observed tropical cyclone strikes and indicates coarse deposits are storm derived. Longer records show tropical cyclone activity was higher from 5000 to 3800 and 2900 to 500 yrs BP. Comparison to records from the North Pacific (out-of-phase) and North Atlantic (in phase) suggests a coordinated pattern of storm activity across tropical cyclone basins over the mid-late Holocene. The changes in tropical cyclone activity we observe in the South Pacific and across other basins may be related to ENSO as well as precession driven changes in ocean-atmosphere thermal gradients.

A statistical procedure for estimating the risk of strong winds from hurricanes, known as the Hurricane Risk Calculator, is demonstrated and applied to several major cities in Louisiana. The procedure provides an estimate of wind risk over different length periods and can be applied to any location experiencing this hazard. Results show that an area 100 km around the city of New Orleans can expect to see hurricane winds blowing at 49 ms−1 (44.3–53.7) [90 % confidence interval (CI)] or stronger, on average, once every 20 years. In comparison, for the same time period, the capital city of Baton Rouge and the surrounding area can expect to see hurricane winds of 43 ms−1 (38.2–47.8) (90 % CI) or stronger. Hurricane track direction is also analyzed at the cities of interest. For Morgan City, Lafayette, Lake Charles, and Alexandria, tropical cyclones with winds at least 18 ms−1 travel from the southeast to northwest. New Orleans and Baton Rouge tropical cyclones have a greater tendency to turn toward the east while within 100 km of the city, historically giving them a southwesterly approach. Tropical cyclones within 350 km off the south-central Louisiana coast occur most often in September, and the most extreme of these events are becoming stronger through time as shown with quantile regression.

The 2011 Atlantic season was marked by above-average tropical cyclone activity with the formation of 19 tropical storms. Seven of the storms became hurricanes and four became major hurricanes (category 3 or higher on the Saffir–Simpson hurricane wind scale). The numbers of tropical storms and hurricanes were above the long-term averages of 12 named storms, 6 hurricanes, and 3 major hurricanes. Despite the high level of activity, Irene was the only hurricane to hit land in 2011, striking both the Bahamas and the United States. Other storms, however, affected the United States, eastern Canada, Central America, eastern Mexico, and the northeastern Caribbean Sea islands. The death toll from the 2011 Atlantic tropical cyclones is 80. National Hurricane Center mean official track forecast errors in 2011 were smaller than the previous 5-yr means at all forecast times except 120 h. In addition, the official track forecast errors set records for accuracy at the 24-, 36-, 48-, and 72-h forecast times. The mean intensity forecast errors in 2011 ranged from about 6 kt (~3 m s−1) at 12 h to about 17 kt (~9 m s−1) at 72 and 120 h. These errors were below the 5-yr means at all forecast times.