SUPPLEMENTAL INFORMATION...IN GREATER DEPTH

To complement the Daily Summary for Monday, 1 December 2014

MONITORING THE HURRICANE FACTOR --
THE 2014 HURRICANE SEASON


Today (1 December 2014) signals the end of the official 2014 hurricane season in the North Atlantic basin (which includes the Gulf of Mexico and the Caribbean), the Eastern North Pacific basin (a region extending from the western coast line of North America westward to a longitude of 140 degrees west) and the Central North Pacific basin (westward to the International Dateline). While a hurricane or other tropical cyclone may develop after 30 November, such an event is rare. In the North Atlantic, the latest recorded hurricane was on 31 December 1954, while on 31 December 2005 Tropical Storm Zeta formed and continued into the new year. The earliest recorded Atlantic hurricane for a season was an unnamed hurricane on 7 March 1908. In the eastern North Pacific basin, the latest hurricane of the season was Hurricane Winnie, which became a Category-1 hurricane on 6 December 1983 and dissipated a day later, while the earliest hurricane of the season for that basin was Hurricane Alma, a category-1 hurricane on the Saffir-Simpson Scale that formed on 12 May 1990 and reached hurricane status on the 15th.

ATLANTIC BASIN

In terms of the number of named tropical cyclones, the just-completed Atlantic hurricane season had a moderate season across the North Atlantic basin as eight tropical cyclones became named systems in 2014. Six of these named tropical cyclones developed into hurricanes (with maximum sustained winds in excess of 74 mph).Two of these hurricanes became major hurricanes (Category 3 or higher on the Saffir-Simpson Hurricane Intensity Scale), with Edouard becoming a category-3 hurricane in mid-September and Gonzalo reaching category-4 status in mid-October.

The first named tropical system of the 2014 Atlantic season was Hurricane Arthur that formed off central Florida's Atlantic coast on 1 July. As of this writing, the last tropical cyclone was Tropical Storm Hanna, which formed over the western Caribbean from the remnants of a tropical depression that had been over the Gulf of Campeche several days earlier. After being a minimal tropical storm for less than 24 hours, Hanna made landfall along the Nicaragua-Honduras border on 27 October. Hurricane Arthur, which became a category 2 hurricane, was the only named tropical cyclone to make landfall along the continental United States in 2014, tracking across the Outer Banks of North Carolina on the 4th of July.

Additional information concerning several of the individual tropical cyclones during this season will be found at http://www.nhc.noaa.gov/data/tcr/index.php?season=2014 with a map showing the tracks of these systems across the basin. More details should appear late next week, as the final version of the North Atlantic summary is prepared.

EASTERN NORTH PACIFIC BASIN

In the eastern North Pacific, the hurricane season runs from 15 May to 30 November. The 2014 hurricane season had 20 named tropical cyclones, with 15 reaching hurricane status. Eight hurricanes became major category 3 hurricanes, with Hurricanes Genevieve and Marie reaching category 5 status. In addition, one tropical depression formed in the basin. The first tropical cyclone in the eastern Pacific during 2014 was category-4 Hurricane Amanda, which formed in late May, while the last tropical cyclone was category-2 Hurricane Vance, which dissipated during the first week of November. While most of the tropical systems remained well off the coasts of Mexico and Central America, Tropical Storms Boris and Trudy made landfall along the coast of southwestern Mexico, while farther to the north, category-4 Hurricane Odile made landfall on Mexico's Baja California Peninsula and category-2 Hurricane Vance made landfall along the central Mexican coast. The remnants of two hurricanes (Odile and Simon) spread much-needed rain across the parts of the Southwestern United States. Three named tropical cyclones that formed in the eastern North Pacific Basin eventually traveled westward and entered into the central North Pacific Basin. Category-4 Hurricane Iselle made landfall on the Big Island of Hawaii, while category-3 Hurricane Julio passed to the north of the Hawaiian Islands.

For additional information concerning some of these tropical cyclones including a map of their tracks across the basin, see http://www.nhc.noaa.gov/data/tcr/index.php?season=2014&basin=epac. More details should be forthcoming in the Eastern North Pacific summary.

CENTRAL NORTH PACIFIC BASIN

The region of the North Pacific Ocean lying between 140 degrees west and the International Dateline (180 degrees longitude) is identified as the Central North Pacific Basin. The hurricane season for this basin officially begins on 1 June and ends on 30 November. The region is monitored by the National Weather Service Forecast Office in Honolulu, which activates the Central Pacific Hurricane Center (CPHC) when tropical cyclone activity becomes imminent in this basin.

During the 2014 season, five named tropical cyclones moved across the central North Pacific. Hurricanes Genevieve, Iselle and Julio entered the central Pacific basin from the eastern Pacific. Tropical Storm Wali and Hurricane Ana formed in the central Pacific. Hurricane Iselle was the strongest tropical cyclone on record to strike the Big Island of Hawaii. Hurricane Ana traversed the basin over 13 days, making it the longest-lived tropical cyclone in the central Pacific during the satellite era. For additional information concerning tropical cyclones in the Central North Pacific, see http://www.prh.noaa.gov/cphc/tcpages/archive.php.

PERSPECTIVE

The eight named tropical cyclones that formed during the 2014 North Atlantic hurricane season meant that the season was less active than average, as a typical North Atlantic hurricane season would have slightly more than ten named systems, based upon long-term averages running from 1931 to 2010. However, the six hurricanes in 2014 tied the number of nearly six hurricanes for the last 80 years, while the two tropical storms were less than the average of slightly more than four tropical storms. In the record 2005 season, 28 named systems formed, with 13 classified as hurricanes and eight tropical storms; seven of the hurricanes during that year became major hurricanes. The least active season in recent history was 1983 when only four named tropical cyclones were reported (three hurricanes and one tropical storm). In 2013 only two hurricanes formed.

Hurricane forecasters suggest that the reason for the relatively quiet 2014 Atlantic hurricane season was a combination of several factors. Strong vertical wind shear (rapid changes in wind speed and/or direction with altitude) and sinking motion in the mid-troposphere across the tropical North Atlantic and the Caribbean that resulted in increased atmospheric stability contributed to reduced tropical cyclone activity in the basin. Drier air across the tropical Atlantic along with a below average West African monsoon also resulted in few African easterly waves that would typically produce tropical cyclones.

Hurricane experts Professor William Gray and Philip Klotzbach from Colorado State University in Fort Collins have been issuing long-range hurricane forecasts for more than two decades. Their forecasts are based upon several factors that include analysis of the wind field at several levels, the rainfall over West Africa and the effects of El Niņo. For additional information on these forecasts, refer to http://tropical.atmos.colostate.edu/forecasts/. In early April 2014, this team released their forecast of the 2014 North Atlantic hurricane season. At that time, they thought that the season would be less active than average due to several factors that included the anticipated development of an El Niño event during the Northern Hemisphere summer and autumn and to an anomalous cooling of the tropical Atlantic last spring. Both of these factors typically suppress Atlantic hurricane activity. In their April forecast, the forecasters called for nine named tropical cyclones, with three potentially becoming hurricanes. One of these hurricanes had been expected to become severe, reaching category 3 or higher on the Saffir-Simpson Scale. They also anticipated a below-average probability of a major Atlantic hurricane making landfall somewhere along the coast of the coterminous US and in the Caribbean. Their final updated forecast at the end of July called for 10 named storms and four hurricanes, one of which would have become a major hurricane.

In mid-May forecasters with NOAA's Climate Prediction Center also generated an outlook for the 2014 Atlantic hurricane season. They foresaw a below-normal hurricane season, giving a 70-percent chance that the basin could experience 8 to 13 named tropical cyclones, with three to six hurricanes. They felt that one to two hurricanes could become major hurricanes. These numbers were adjusted slightly in an August update.

The 2014 season in the eastern North Pacific tied 1990 for being the fourth most active season on record with twenty named systems. This number was above the long-term (1966-2012) average of slightly more than 15 named tropical cyclones. The 15 hurricanes in 2014 ranked second behind 1990 (with 16 hurricanes) over the last 49 years, well above the long-term average of slightly more than eight hurricanes per annum.

The 2014 season in Central North Pacific basin with five named tropical cyclones was relatively active compared to the long-term average. Over the last 60 years, nearly three named tropical cyclones either develop or enter this basin from the east. The four hurricanes that traversed the Central Pacific in 2014 was well above the average of one hurricane that typically forms only once in two years. Furthermore, this season was historic as the Hawaiian Islands experienced the effects of three tropical cyclones, including Hurricane Iselle that made landfall on the Big Island.

LOOKING AT LONG-TERM TROPICAL CYCLONE CLIMATOLOGIES

The National Hurricane Center (NHC) has an updated and revised edition of its "Tropical Cyclones of the North Atlantic Ocean, 1851-2006." While a paper copy of this book is available for a cost from NHC, a 243-pg pdf file of this edition can be downloaded for free. NHC also released the first edition of "Tropical Cyclones of the Eastern North Pacific Ocean, 1949-2006." In addition to a paper copy is available for sale, a free 164-page pdf file is available. Both of these climatologies have numerous graphics that show long-term changes in tropical cyclone frequency in the two basins.
A climatology of tropical cyclones in the central North Pacific from the 1950s to 2008 is available from the CPHC climatology website maintained by the Central Pacific Hurricane Center (CPHC) in Honolulu, HI.


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Prepared by Edward J. Hopkins, Ph.D., email
hopkins@meteor.wisc.edu
© Copyright, 2014, The American Meteorological Society.