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Eric S. Blake and Richard J. Pasch

Abstract

The hurricane season of 2008 in the eastern North Pacific basin is summarized, and the individual tropical cyclones are described. Official track and intensity forecasts of these cyclones are also evaluated. The 2008 eastern North Pacific season was relatively quiet, with overall activity at about 75% of the long-term median. A total of 16 tropical storms formed, of which 7 became hurricanes and 2 became major hurricanes. One hurricane, one tropical storm, and two tropical depressions made landfall in Mexico, causing eight direct deaths in that country along with significant property damage. In addition, Tropical Storm Alma was the first tropical cyclone on record to make landfall along the Pacific coast of Nicaragua. On average, the official track forecasts in the eastern Pacific for 2008 were quite skillful and set records for accuracy from 1 to 3 days. However, no appreciable improvement in mean intensity forecast skill was noted.

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Eric S. Blake and William M. Gray

Abstract

Although skillful seasonal hurricane forecasts for the Atlantic basin are now a reality, large gaps remain in our understanding of observed variations in the distribution of activity within the hurricane season. The month of August roughly spans the first third of the climatologically most active part of the season, but activity during the month is quite variable. This paper reports on an initial investigation into forecasting year-to-year variability of August tropical cyclone (TC) activity using the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis dataset. It is shown that 55%–75% of the variance of August TC activity can be hindcast using a combination of 4–5 global predictors chosen from a 12-predictor pool with each of the predictors showing precursor associations with TC activity. The most prominent predictive signal is the equatorial July 200-mb wind off the west coast of South America. When this wind is anomalously strong from the northeast during July, Atlantic TC activity in August is almost always enhanced. Other July conditions associated with active Augusts include a weak subtropical high in the North Atlantic, an enhanced subtropical high in the northwest Pacific, and low pressure in the Bering Sea region.

The most important application of the August-only forecast is that predicted net tropical cyclone (NTC) activity in August has a significant relationship with the incidence of U.S. August TC landfall events. Better understanding of August-only TC variability will allow for a more complete perspective of total seasonal variability and, as such, assist in making better seasonal forecasts.

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Philip J. Klotzbach and Eric S. Blake

Abstract

Both El Niño–Southern Oscillation (ENSO) and the Madden–Julian oscillation (MJO) have been documented in previous research to impact tropical cyclone (TC) activity around the globe. This study examines the relationship of each mode individually along with a combined index on tropical cyclone activity in the north-central Pacific. Approximately twice as many tropical cyclones form in the north-central Pacific in El Niño years compared with La Niña years. These differences are attributed to a variety of factors, including warmer sea surface temperatures, lower sea level pressures, increased midlevel moisture, and anomalous midlevel ascent in El Niño years. When the convectively enhanced phase of the MJO is located over the eastern and central tropical Pacific, the north-central Pacific tends to have more tropical cyclone activity, likely because of reduced vertical wind shear, lower sea level pressures, and increased vertical motion. The convectively enhanced phase of the MJO is also responsible for most of the TCs that undergo rapid intensification in the north-central Pacific. A combined MJO–ENSO index that is primarily associated with anomalous rising motion over the tropical eastern Pacific has an even stronger relationship with north-central Pacific TCs, as well as rapid intensification, than either individually.

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John L. Beven II and Eric S. Blake

Abstract

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.

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Eric S. Blake and Todd B. Kimberlain

Abstract

Overall activity during the 2011 eastern North Pacific hurricane season was near average. Of the 11 tropical storms that formed, 10 became hurricanes and 6 reached major hurricane strength (category 3 or stronger on the Saffir–Simpson hurricane wind scale). For comparison, the 1981–2010 averages are about 15 tropical storms, 8 hurricanes, and 4 major hurricanes. Interestingly, although the number of named storms was below average, the numbers of hurricanes and major hurricanes were above average. The 2011 season had the most hurricanes since 2006 and the most major hurricanes since 1998. Two hurricanes affected the southwestern coast of Mexico (Beatriz as a category 1 hurricane and Jova as a category 2 hurricane), and the season’s tropical cyclones caused about 49 deaths. On average, the National Hurricane Center track forecasts in the eastern North Pacific for 2011 were very skillful.

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John L. Beven II, Lixion A. Avila, Eric S. Blake, Hugh D. Cobb, and Richard J. Pasch

Abstract

The Best Track Change Committee of the National Hurricane Center evaluates proposed changes to the Hurricane Database (HURDAT) in the Atlantic and eastern North Pacific basins. In the companion paper, Gruskin documents a possible tropical cyclone that affected portions of the eastern United States on 27–28 June 2006 and proposes that it be added to HURDAT. The committee reviewed the aircraft, radar, rawinsonde, satellite, and surface data available on this system and found it to be a challenging and complex system. A reconnaissance aircraft flying in the system in real time failed to find a closed circulation before landfall, and kinematic parameters suggest the system was more likely to have the structure of an open wave, with any surface circulation at best being poorly defined. Because of the lack of conclusive evidence regarding the existence of a closed surface circulation before landfall, the committee has decided not to add this system to HURDAT as a tropical cyclone.

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Daniel P. Brown, John L. Beven, James L. Franklin, and Eric S. Blake

Abstract

The 2008 Atlantic hurricane season is summarized and the year’s tropical cyclones are described. Sixteen named storms formed in 2008. Of these, eight became hurricanes with five of them strengthening into major hurricanes (category 3 or higher on the Saffir–Simpson hurricane scale). There was also one tropical depression that did not attain tropical storm strength. These totals are above the long-term means of 11 named storms, 6 hurricanes, and 2 major hurricanes. The 2008 Atlantic basin tropical cyclones produced significant impacts from the Greater Antilles to the Turks and Caicos Islands as well as along portions of the U.S. Gulf Coast. Hurricanes Gustav, Ike, and Paloma hit Cuba, as did Tropical Storm Fay. Haiti was hit by Gustav and adversely affected by heavy rains from Fay, Ike, and Hanna. Paloma struck the Cayman Islands as a major hurricane, while Omar was a major hurricane when it passed near the northern Leeward Islands. Six consecutive cyclones hit the United States, including Hurricanes Dolly, Gustav, and Ike. The death toll from the Atlantic tropical cyclones is approximately 750.

A verification of National Hurricane Center official forecasts during 2008 is also presented. Official track forecasts set records for accuracy at all lead times from 12 to 120 h, and forecast skill was also at record levels for all lead times. Official intensity forecast errors in 2008 were below the previous 5-yr mean errors and set records at 72–120 h.

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Philip J. Klotzbach, Carl J. Schreck III, Jennifer M. Collins, Michael M. Bell, Eric S. Blake, and David Roache

Abstract

The 2017 North Atlantic hurricane season was extremely active, with 17 named storms (1981–2010 median is 12.0), 10 hurricanes (median is 6.5), 6 major hurricanes (median is 2.0), and 245% of median accumulated cyclone energy (ACE) occurring. September 2017 generated more Atlantic named storm days, hurricane days, major hurricane days, and ACE than any other calendar month on record. The season was destructive, with Harvey and Irma devastating portions of the continental United States, while Irma and Maria brought catastrophic damage to Puerto Rico, Cuba, and many other Caribbean islands. Seasonal forecasts increased from calling for a slightly below-normal season in April to an above-normal season in August as large-scale environmental conditions became more favorable for an active hurricane season. During that time, the tropical Atlantic warmed anomalously while a potential El Niño decayed in the Pacific. Anomalously high SSTs prevailed across the tropical Atlantic, and vertical wind shear was anomalously weak, especially in the central tropical Atlantic, from late August to late September when several major hurricanes formed. Late-season hurricane activity was likely reduced by a convectively suppressed phase of the Madden–Julian oscillation. The large-scale steering flow was different from the average over the past decade with a strong subtropical high guiding hurricanes farther west across the Atlantic. The anomalously high tropical Atlantic SSTs and low vertical wind shear were comparable to other very active seasons since 1982.

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John L. Beven II, Lixion A. Avila, Eric S. Blake, Daniel P. Brown, James L. Franklin, Richard D. Knabb, Richard J. Pasch, Jamie R. Rhome, and Stacy R. Stewart

Abstract

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.

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James L. Franklin, Richard J. Pasch, Lixion A. Avila, John L. Beven II, Miles B. Lawrence, Stacy R. Stewart, and Eric S. Blake

Abstract

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.

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