SUPPLEMENTAL INFORMATION...IN GREATER DEPTH

Monday, 24 April 2017

MONITORING THE HURRICANE FACTOR --
THE 2016 HURRICANE SEASON


While many of us have just thought about spring cleaning, hurricane season is right around the corner. In the eastern North Pacific, covering a region extending from the western coast line of North America westward to a longitude of 140 degrees west, the official 2017 Pacific hurricane season defined by the National Hurricane Center will commence three weeks from today (15 May, to be precise). In slightly more than five weeks, the official 2017 Atlantic hurricane season will start on 1 June in the North Atlantic basin, which includes the Gulf of Mexico and the Caribbean. The hurricane season in the Central North Pacific basin (from 140 degrees west to the International Dateline) also starts on 1 June.

Although a hurricane or other tropical cyclone may develop before these official start dates, such an event would be rare. Considering the period of record in the North Atlantic that extends back to 1851, the earliest recorded hurricane for any year was Hurricane Alex, which became a hurricane last year on 14 January 2016. Previously, an unnamed hurricane that formed on 7 March 1908 had been considered to be the earliest to form in a calendar year. The official end to the hurricane season is on 30 November, but the latest recorded hurricane for a year was the second Hurricane Alice of the year on 31 December 1954. Interestingly, Tropical Storm Zeta, formed on 31 December 2005 and continued into the new year.

In the eastern North Pacific basin, the earliest hurricane of the season for that basin on record (since 1949) 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, which coincides with the start of the hurricane season in that basin. On the other hand, the latest hurricane of the season was Hurricane Winnie, which became a Category-1 hurricane on 6 December 1983 and dissipated a day later.

In the central North Pacific basin, the earliest hurricane to form during modern times (since 1957) was Hurricane Pali on 11 January 2016. This hurricane was earlier than Hurricane Ekeka that formed on 28 January 1992. The latest central Pacific hurricane to have formed in a season during modern times was Hurricane Iwa, which reached hurricane strength on 23 November 1983.

ATLANTIC BASIN

The 2016 Atlantic hurricane season was more active than average as fifteen tropical cyclones became named systems. Seven of these named tropical cyclones developed into hurricanes (with maximum sustained winds in excess of 74 mph). Three of these hurricanes became major hurricanes (category-3 or higher on the Saffir-Simpson Hurricane Intensity Scale), with Gaston becoming a category-3 hurricane in late August, Matthew strengthening to category-5 status at the end of September and Nicole reaching category-4 status in early October. Because of their intensity and destructiveness during the 2016 season, the World Meteorological Organization (WMO) Region IV Hurricane Committee retired the names of Matthew and Otto from their internationally recognized Atlantic list of hurricane names. These names represent the 81st and 82nd names that have been retired.

The first named tropical system of the 2016 Atlantic season was Hurricane Alex that became a category 1 hurricane over the far eastern Atlantic approximately 500 miles south of the central Azores on 14 January after originally forming as a subtropical storm. Furthermore, Alex was the earliest hurricane to form in the Atlantic basin since records began over 160 years ago. The last tropical cyclone of 2016 was Hurricane Otto, which formed approximately 300 miles from the Nicaraguan coast on 22 November and became a category-2 hurricane before making landfall along the coast of southern Nicaragua on 24 November. Apparently, Otto was the latest hurricane in any calendar year on record to make a landfall in the entire Atlantic basin.

Two hurricanes made landfall along the coast of the United States in 2016. Hurricane Hermine made landfall as a category-1 hurricane along the Florida Panhandle on 2 September and then traveled to the northeast across southern Georgia and the coasts of the Carolinas. Later, Hurricane Matthew, which had become a major category 5 hurricane earlier, made landfall along the South Carolina coast near Myrtle Beach as a minimal category 1 hurricane after paralleling Florida's Atlantic Coast. In addition, Tropical Storm Julia formed near Jacksonville along the northeast coast of Florida on 13 September, which represents one of the rare times that a tropical storm has formed over land. Moving northward, Julia remained close to the Georgia and South Carolina coasts before turning out to sea.

Additional information concerning several of the individual tropical cyclones during this 2016 can be found at http://www.nhc.noaa.gov/data/tcr/index.php?season=2016&basin=atl with a map showing the tracks of these systems across the basin.

EASTERN NORTH PACIFIC BASIN

In the eastern North Pacific, the hurricane season runs from 15 May to 30 November. The 2015 hurricane season had 18 named tropical cyclones, with 13 reaching hurricane status. Nine hurricanes became major (category-3 or greater) hurricanes, with Hurricane Patricia reaching category 5 status. Strengthening from a tropical storm to a category 5 hurricane in slightly more than 24 hours, Patricia had the distinction of being the strongest hurricane on record for the eastern North Pacific basin as well as the Western Hemisphere. Maximum sustained surface winds surrounding Patricia reached 200 mph and the minimum central pressure fell to 880 mb (or 25.99 inches of mercury). The nine major hurricanes in 2015 represents the greatest number of major hurricanes since reliable records began in 1971. In addition, five unnamed tropical depressions formed in the basin.

In the eastern North Pacific, the hurricane season runs from 15 May to 30 November. The 2016 hurricane season had 20 named tropical cyclones, with 10 reaching hurricane status. Five hurricanes became major (category-3 or greater) hurricanes, three of which reached category 4 status (Hurricanes Lester, Madeline and Seymour.)
The first named tropical cyclone in the eastern Pacific during 2016 was Tropical Storm Agatha, which formed in early July nearly 800 miles to the southwest of the southern tip of Mexico's Baja California Peninsula. The last tropical cyclone was Tropical Storm Otto, which had originally formed over the Caribbean Sea in the North Atlantic basin and then crossed over Central America to emerge as a tropical storm in the eastern North Pacific on 25 November.
While most of the tropical systems in 2016 remained well off the coasts of Mexico and Central America, category-1 hurricane Newton made landfall along the central coast of Mexico's Baja California Peninsula. Tropical Storm Javier brushed along the coast near the southern tip of Baja California.

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=2016&basin=epac. More details can be found 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 2016 season, two hurricanes (Pali and Ulika) formed in the central North Pacific basin. Pali was the first tropical cyclone of the year, having formed in January. Hurricane Ulika was the last named system to form in the basin, as it formed on 9 September and finally dissipated on 30 September, after making several crossings of the 140 degrees west meridian that represents the boundary between the central and eastern Pacific basins. In addition to these two hurricanes, five additional named systems that included two hurricanes (Lester and Madeline), two tropical storms (Ceclia and Darby) and a tropical depression (Ivette) entered the central Pacific basin from the eastern Pacific. Hurricanes Lester and Madeline approached the Hawaiian Islands, but neither made landfall on any of the islands. For additional information concerning tropical cyclones in the Central North Pacific, see http://www.prh.noaa.gov/cphc/tcpages/archive.php.

PERSPECTIVE

The fifteen named tropical cyclones that formed during the 2016 North Atlantic hurricane season meant that the season was more 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. Furthermore, the seven hurricanes in 2016 were slightly more than the average number of six per annum for the last 80 years, as were the eight tropical storms that were more than the long-term annual average of nearly five tropical storms. By comparison, the record 2005 season had 28 named systems, with 13 classified as hurricanes and eight tropical storms; seven of the hurricanes during that year became major hurricanes. Conversely, the least active season in recent history was 1983 when only four named tropical cyclones were reported (three hurricanes and one tropical storm). Only two hurricanes formed in 1982 and 2013, which represent the two years with the fewest hurricanes since 1931.

The late Professor William Gray and Philip Klotzbach, hurricane experts from Colorado State University in Fort Collins, have been issuing long-range Atlantic 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 Niño. For additional information on these forecasts, refer to http://tropical.atmos.colostate.edu/forecasts/. Earlier this month, the forecast team from Colorado State University released its initial "Extended Range Forecast of 2017 Atlantic Seasonal Hurricane Activity" that provides projected estimates of the number of named tropical cyclones during the upcoming 2017 hurricane season. The team foresees slightly below-average tropical cyclone activity during this upcoming hurricane season. The team's initial April forecast envisions eleven named tropical cyclones, which include four hurricanes. Of these hurricanes, the forecasters foresee two major hurricanes (category 3 or higher on the Saffir-Simpson Scale). A below-average probability is anticipated for major hurricanes making landfall along the United States coastline and in the Caribbean. The team bases their outlook on the likelihood that the current ENSO-neutral conditions would evolve into either weak or moderate El NiƱo conditions by early autumn during the peak in the Atlantic hurricane season. Furthermore, the waters of the tropical Atlantic have anomalously cooled over the past month and the far North Atlantic is relatively cold, potentially indicative of a negative phase of the Atlantic Multi-Decadal Oscillation.

The 2016 season in the eastern North Pacific with 19 named systems was more active than the long-term (1966-2012) average of slightly more than 15 named tropical cyclones. The 10 hurricanes in 2016 was also above the long-term average of slightly more than eight hurricanes per annum. The five major hurricanes in 2016 exceeded the long-term average of slightly more than four in a year. CPC forecasters should provide their outlook for the 2017 eastern Pacific hurricane season by mid-May..

The 2016 season in Central North Pacific basin with seven named tropical cyclones was 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 on average and an average of one hurricane that typically forms only once in two years. CPC forecasters in May 2016 had issued an outlook for the central North Pacific basin with activity ranging from near- to above-average. Four to seven tropical cyclones were expected to affect the central North Pacific in 2016, either forming within the basin or entering it from the Eastern Pacific. The forecasters voiced some uncertainty in their outlooks due to an anticipated transition to La Niña conditions, along with changes in global sea surface temperatures across the Pacific and Atlantic Oceans. An outlook for the 2017 season in the central Pacific basin should be provided by CPC in May.

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 that is available for sale, a free 164-page pdf file is available online. 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 2013 is available from the CPHC climatology website maintained by the Central Pacific Hurricane Center (CPHC) in Honolulu, HI. A compilation of individual tropical cyclones in the central Pacific is also available by year extending back to 1957, along with notable systems dating back into the 19th century.


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Prepared by Edward J. Hopkins, Ph.D., email hopkins@aos.wisc.edu
© Copyright, 2017, The American Meteorological Society.