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The National Hurricane Center (NHC) uses a variety of guidance models for its operational tropical cyclone track, intensity, and wind structure forecasts, and as baselines for the evaluation of forecast skill. A set of the simpler models, collectively known as the NHC guidance suite, is maintained by NHC. The models comprising the guidance suite are briefly described and evaluated, with details provided for those that have not been documented previously. Decay-SHIFOR is a modified version of the Statistical Hurricane Intensity Forecast (SHIFOR) model that includes decay over land; this modification improves the SHIFOR forecasts through about 96 h. T-CLIPER, a climatology and persistence model that predicts track and intensity using a trajectory approach, has error characteristics similar to those of CLIPER and D-SHIFOR but can be run to any forecast length. The Trajectory and Beta model (TAB), another trajectory track model, applies a gridpoint spatial filter to smooth winds from the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) model. TAB model errors were 10%–15% lower than those of the Beta and Advection model (BAM), the model it replaced in 2017. Optimizing TAB's vertical weights shows that the lower troposphere's environmental flow provides a better match to observed tropical cyclone motion than does the upper troposphere's, and that the optimal steering layer is shallower for higher-latitude and weaker tropical cyclones. The advantages and disadvantages of the D-SHIFOR, T-CLIPER, and TAB models relative to their earlier counterparts are discussed. Significance Statement: This paper provides a comprehensive summary and evaluation of a set of simpler forecast models used as guidance for NHC's operational tropical cyclone forecasts, and as baselines for the evaluation of forecast skill; these include newer techniques that extend forecasts to 7 days and beyond. [ABSTRACT FROM AUTHOR]

'Best tracks' are National Hurricane Center (NHC) poststorm analyses of the intensity, central pressure, position, and size of Atlantic and eastern North Pacific basin tropical and subtropical cyclones. This paper estimates the uncertainty (average error) for Atlantic basin best track parameters through a survey of the NHC Hurricane Specialists who maintain and update the Atlantic hurricane database. A comparison is then made with a survey conducted over a decade ago to qualitatively assess changes in the uncertainties. Finally, the implications of the uncertainty estimates for NHC analysis and forecast products as well as for the prediction goals of the Hurricane Forecast Improvement Program are discussed. [ABSTRACT FROM AUTHOR]

Tropical cyclone intensity change remains a forecasting challenge with important implications for such vulnerable areas as the U.S. coast along the Gulf of Mexico. Analysis of 1979-2008 Gulf tropical cyclones during their final two days before U.S. landfall identifies patterns of behavior that are of interest to operational forecasters and researchers. Tropical storms and depressions strengthened on average by about 7 kt for every 12 h over the Gulf, except for little change during their final 12 h before landfall. Hurricanes underwent a different systematic evolution. In the net, category 1-2 hurricanes strengthened, while category 3-5 hurricanes weakened such that tropical cyclones approach the threshold of major hurricane status by U.S. landfall. This behavior can be partially explained by consideration of the maximum potential intensity modified by the environmental vertical wind shear and hurricane-induced sea surface temperature reduction near the storm center associated with relatively low oceanic heat content levels. Linear least squares regression equations based on initial intensity and time to landfall explain at least half the variance of the hurricane intensity change. Applied retrospectively, these simple equations yield relatively small forecast errors and biases for hurricanes. Characteristics of most of the significant outliers are explained and found to be identifiable a priori for hurricanes, suggesting that forecasters can adjust their forecast procedures accordingly. [ABSTRACT FROM AUTHOR]

The 2006 Atlantic hurricane season is summarized and the year’s tropical cyclones are described. A verification of National Hurricane Center official forecasts during 2006 is also presented. Ten cyclones attained tropical storm intensity in 2006. Of these, five became hurricanes and two became “major” hurricanes. Overall activity was near the long-term mean, but below the active levels of recent seasons. For the first time since 2001, no hurricanes made landfall in the United States. Elsewhere in the basin, hurricane-force winds were experienced in Bermuda (from Florence) and in the Azores (from Gordon). Official track forecast errors were smaller in 2006 than during the previous 5-yr period (by roughly 15%–20% out to 72 h), establishing new all-time lows at forecast projections through 72 h. Since 1990, 24–72-h official track forecast errors have been reduced by roughly 50%. [ABSTRACT FROM AUTHOR]

The 2005 Atlantic hurricane season was the most active of record. Twenty-eight storms occurred, including 27 tropical storms and one subtropical storm. Fifteen of the storms became hurricanes, and seven of these became major hurricanes. Additionally, there were two tropical depressions and one subtropical depression. Numerous records for single-season activity were set, including most storms, most hurricanes, and highest accumulated cyclone energy index. Five hurricanes and two tropical storms made landfall in the United States, including four major hurricanes. Eight other cyclones made landfall elsewhere in the basin, and five systems that did not make landfall nonetheless impacted land areas. The 2005 storms directly caused nearly 1700 deaths. This includes approximately 1500 in the United States from Hurricane Katrina—the deadliest U.S. hurricane since 1928. The storms also caused well over $100 billion in damages in the United States alone, making 2005 the costliest hurricane season of record. [ABSTRACT FROM AUTHOR]

The 2005 eastern North Pacific hurricane season is summarized, the individual tropical cyclones are described, and official track and intensity forecasts are verified and evaluated. The season’s overall activity was, by most measures, below average. While a near-average 15 tropical storms formed, many of them were relatively weak and short-lived. Seven of these storms became hurricanes, but only one reached major hurricane status (an intensity of 100 kt or greater on the Saffir–Simpson hurricane scale) in the eastern North Pacific basin. One of the hurricanes, Adrian, approached Central America in May but weakened to a tropical depression prior to landfall. Adrian was the only eastern North Pacific tropical cyclone to make landfall during 2005, and it was directly responsible for one fatality. [ABSTRACT FROM AUTHOR]

The article reports on the Atlantic hurricane season in 2006. The author said that there were 10 tropical storms in 2006. 5 of these became hurricanes and 2 of which became major hurricanes. All the hurricane activity took place during a 37-day period between August 27 and October 2. The tropical storm Alberto formed in the northwestern Caribbean Sea on June 10. An unnamed tropical cyclone formed along the end of a cold front that moved offshore of the northeastern U.S. late on July 13.

The 2004 Atlantic hurricane season is summarized, and the year’s tropical and subtropical cyclones are described. Fifteen named storms, including six “major” hurricanes, developed in 2004. Overall activity was nearly two and a half times the long-term mean. The season was one of the most devastating on record, resulting in over 3100 deaths basinwide and record property damage in the United States. [ABSTRACT FROM AUTHOR]

The 2004 eastern North Pacific hurricane season is reviewed. It was a below-average season in terms of number of systems and landfalls. There were 12 named tropical cyclones, of which 8 became hurricanes. None of the tropical storms or hurricanes made landfall, and there were no reports of deaths or damage. A description of each cyclone is provided, and track and intensity forecasts for the season are evaluated. [ABSTRACT FROM AUTHOR]

The 2003 Atlantic hurricane season is described. The season was very active, with 16 tropical storms, 7 of which became hurricanes. There were 49 deaths directly attributed to this year’s tropical cyclones. [ABSTRACT FROM AUTHOR]

The tropical cyclone activity for 2003 in the eastern North Pacific hurricane basin is summarized. Activity during 2003 was slightly below normal. Sixteen tropical storms developed, seven of which became hurricanes. However, there were no major hurricanes in the basin for the first time since 1977. The first hurricane did not form until 24 August, the latest observed first hurricane at least since reliable satellite observations began in 1966. Five tropical cyclones made landfall on the Pacific coast of Mexico, resulting in 14 deaths. [ABSTRACT FROM AUTHOR]

Presents information on several hurricanes and tropical storms which have hit the U.S. in 2004. Hurricane Alex; Tropical Storm Bonnie; Hurricane Danielle; Hurricane Frances; Hurricane Ivan.

Discusses the article "Exaggeration of Wind Conditions in Hurricane Floyd and Other Tropical Cyclones," by Peter R. Sparks, concerning the statement issued by the U.S. National Oceanic and Atmospheric Administration's National Hurricane Center (NHC) regarding the Hurricane Floyd in September 1999. Allegations against the statement; Overview of the advisory issued by NHC for Hurricane Floyd on September 16; Analysis of NHC hurricane advisory/forecast.

The 1999 hurricane season in the eastern North Pacific is summarized, and individual tropical storms and hurricanes are described. Producing only nine named storms, the season tied 1996 as the second least active on record. Hurricane Dora was the strongest and longest-lived cyclone of the season. Hurricane Greg, the only cyclone to make landfall during the season, weakened to a tropical storm just before moving ashore in Baja California, Mexico. Fifteen deaths resulted from the tropical cyclones. [ABSTRACT FROM AUTHOR]

The 2002 eastern North Pacific hurricane season is summarized and the year's tropical cyclones are described. The season featured 12 named tropical storms, of which 6 became hurricanes. Five of the six hurricanes reached an intensity of 100 kt or higher. There were two landfalling cyclones, Tropical Storm Julio and Hurricane Kenna. Kenna, which made landfall near San Blas, Mexico, with winds of near 120 kt, was responsible for four deaths. [ABSTRACT FROM AUTHOR]

Activity during the 2001 hurricane season was similar to that of the 2000 season. Fifteen tropical storms developed, with nine becoming hurricanes and four major hurricanes. Two tropical depressions failed to become tropical storms. Similarities to the 2000 season include overall activity much above climatological levels and most of the cyclones occurring over the open Atlantic north of 25°N. The overall "lateness" of the season was notable, with 11 named storms, including all the hurricanes, forming after 1 September. There were no hurricane landfalls in the United States for the second year in a row. However, the season's tropical cyclones were responsible for 93 deaths, including 41 from Tropical Storm Allison in the United States, and 48 from Hurricanes Iris and Michelle in the Caribbean. [ABSTRACT FROM AUTHOR]

Focuses on the hurricanes that developed in the eastern North Pacific region in 2002. Hurricane Alma originated from a tropical wave across the western coast of Africa; Tropical storm Boris developed from the interaction of an Atlantic tropical wave; Hurricane Kenna originated from a disturbance across Central America.

The recent development of the global positioning system (GPS) dropwindsonde has allowed the wind and thermodynamic structure of the hurricane eyewall to be documented with unprecedented accuracy and resolution. In an attempt to assist operational hurricane forecasters in their duties, dropwindsonde data have been used in this study to document, for the first time, the mean vertical profile of wind speed in the hurricane inner core from the surface to the 700-hPa level, the level typically flown by reconnaissance aircraft. The dropwindsonde-derived mean eyewall wind profile is characterized by a broad maximum centered 500 m above the surface. In the frictional boundary layer below this broad maximum, the wind decreases nearly linearly with the logarithm of the altitude. Above the maximum, the winds decrease because of the hurricane's warm core. These two effects combine to give a surface wind that is, on average, about 90% of the 700-hPa value. The dropwindsonde observations largely confirm recent operational practices at the National Hurricane Center for the interpretation of flight-level data. Hurricane wind profiles outside of the eyewall region are characterized by a higher level of maximum wind, near 1 km, and a more constant wind speed between 700 hPa and the top of the boundary layer. Two factors that likely affect the eyewall profile structure are wind speed and vertical motion. A minimum in surface wind adjustment factor (i.e., relatively low surface wind speeds) was found when the wind near the top of the boundary layer was between 40 and 60 m s[SUP-1]. At higher wind speeds, the fraction of the boundary layer wind speed found at the surface increased, contrary to expectation. Low-level downdrafts, and enhanced vertical motion generally, were also associated with higher relative surface winds. These results may be of interest to engineers concerned with building codes, to emergency managers who may be tempted to use high-rise buildings as a "refuge of... [ABSTRACT FROM AUTHOR]

The 2001 eastern North Pacific hurricane season is reviewed. It was a near-average season in terms of the number of systems, with 15 named tropical cyclones of which 8 became hurricanes. One tropical cyclone made landfall in Mexico and two reached category 3 or higher on the Saffir-Simpson hurricane scale. A description of each named cyclone is provided, and track and intensity forecasts for the season are evaluated. [ABSTRACT FROM AUTHOR]

The 2000 Atlantic hurricane season is summarized and the year's tropical and subtropical cyclones are described. While overall activity was very high compared to climatology, with 15 cyclones attaining tropical (or subtropical) storm intensity, much of this activity occurred outside of the deep Tropics, over open waters north of 25°N. The season's tropical cyclones were responsible for 54 fatalities, with most of these occurring in Central America in association with Hurricanes Gordon and Keith. [ABSTRACT FROM AUTHOR]

There were 11 tropical storms, 6 hurricanes, and 2 tropical depressions during the 2000 eastern North Pacific hurricane season. Two tropical storms made landfall in Mexico. [ABSTRACT FROM AUTHOR]

The 1999 Atlantic basin hurricane season produced 4 tropical storms and 8 hurricanes for a total of 12 named tropical cyclones. Seven of these affected land. Hurricane Floyd—the deadliest U.S. hurricane since Agnes in 1972—caused a disastrous flood event over the U.S. mid-Atlantic and northeastern coastal states, resulting in 56 U.S. deaths and 1 death in the Bahamas. Heavy rain from a tropical depression contributed to some 400 inland flood deaths in Mexico. [ABSTRACT FROM AUTHOR]

Presents information on a study pertaining to atmospheric chemistry while examining the validity of the traditional balance approximation in hurricanes. Observations of the study; Reference to the wind observations of the hurricane Gloria of 1985; Discussion and conclusions of the study.

Although some recent progress has been made in operational tropical cyclone (TC) intensity forecasting, the prediction of rapid intensification (RI) remains a challenging problem. To document RI forecast progress, deterministic and probabilistic operational intensity models used by the National Hurricane Center (NHC) are briefly reviewed. Results show that none of the deterministic models had RI utility from 1991 to about 2015 due to very low probability of detection, very high false alarm ratio, or both. Some ability to forecast RI has emerged since 2015, with dynamical models being the best guidance for the Atlantic and statistical models the best RI guidance for the eastern North Pacific. The first probabilistic RI guidance became available in 2001, with several upgrades since then leading to modest skill in recent years. A tool introduced in 2018 (DTOPS) is currently the most skillful among NHC's probabilistic RI guidance. To measure programmatic progress in forecasting RI, the Hurricane Forecast Improvement Program has introduced a new RI metric that uses the traditional mean absolute error but restricts the sample to only those cases where RI occurred in the verifying best track or was forecast. By this metric, RI forecasts have improved by ~20–25% since the 2015–2017 baseline period. [ABSTRACT FROM AUTHOR]