SUPPLEMENTAL INFORMATION...IN GREATER DEPTH

Monday, 28 November 2016

MONITORING THE HURRICANE FACTOR --
THE 2016 HURRICANE SEASON


This coming Wednesday (30 November 2016) signals the end of the official 2016 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 named tropical cyclone (hurricane or tropical storm) may develop in these basins after 30 November, such an event is rare. Considering the period of record in the North Atlantic that extends back to 1851, the latest recorded hurricane was the second Hurricane Alice of the year 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 any season was Hurricane Alex, which formed earlier this year on 14 January 2016.
In the eastern North Pacific basin, the latest hurricane of the season of record (since 1949) was Hurricane Winnie, which became a category-1 hurricane (on the Saffir-Simpson Scale) 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 that formed on 12 May 1990 and reached hurricane status on the 15th.
In the central North Pacific basin, the latest hurricane to have formed in a season during modern times (since 1957) was Hurricane Iwa, which reached hurricane strength on 23 November 1983. On the other hand, the earliest hurricane to form in the central Pacific was Hurricane Pali that formed earlier this current year on 11 January.

ATLANTIC BASIN

The current Atlantic hurricane season has been more active than average as fifteen tropical cyclones became named systems as of late November. 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.
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. As of this writing, the last tropical cyclone of this season 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 season will be found at http://www.nhc.noaa.gov/data/tcr/index.php?season=2016&basin=atl with a preliminary map showing the tracks of these systems across the basin. More details should appear in the next few weeks, 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. As of the last week of 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 (as of the time of this writing) was Tropical Storm Otto, which had originally formed over the Caribbean Sea in the North Atlantic basin and had crossed over Central America and emerged as a tropical storm in the eastern North Pacific on 25 November.
While most of the tropical systems 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 preliminary map of their tracks across the basin, see http://www.nhc.noaa.gov/data/tcr/index.php?season=2016&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 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. As of this time, 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/. In early April 2016, the team released its initial forecast of the 2016 North Atlantic hurricane season. In this initial forecast, a season with approximately average tropical cyclone activity was anticipated with twelve named tropical cyclones following the early development of Hurricane Alex in January; five additional hurricanes were anticipated, with two of these possibly becoming major hurricanes. At that time, the outlook was based on the continued weakening of the 2015-16 El Niño event during late boreal spring, followed by a transition to ENSO-neutral conditions or possibly La Niña conditions by the peak of the Atlantic hurricane season in early to mid September. The relatively warm waters of the tropical Atlantic coupled with a quite cold far North Atlantic were considered, a situation indicative of a negative phase of the Atlantic Multi-Decadal Oscillation.
Klotzbach issued a final updated forecast in August that called for a total of 15 named tropical cyclones for the entire 2016 season, six of which could become hurricanes.
Forecasters with NOAA's Climate Prediction Center (CPC) also generated an outlook for the 2016 Atlantic hurricane season in mid-May. They foresaw a near-normal hurricane season, giving a 70-percent chance that the basin could experience ten to sixteen named tropical cyclones.  The forecasters also felt that four to eight tropical cyclones could become hurricanes, with as many as four of these hurricanes possibly becoming major hurricanes. The forecasters claimed that prediction of the frequency of named tropical cyclones in the North Atlantic basin had been made difficult by the forecast uncertainty in the climate signals involving the end of the period of high activity in the basin that began in 1995, the timing of the transition from ENSO-neutral to conditions La Niña and the presence of a warm 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. In May 2016 CPC forecasters had issued an outlook for the eastern North Pacific basin that called for a near-normal hurricane season with a 70-percent chance of the formation of between 13 and 20 named tropical cyclones, six to eleven of which would be hurricanes. Between three and six major hurricanes (category 3 or higher) were also envisioned. The forecasters indicated that the anticipated transition from an El Niño to a La Niña event, along with global patterns of sea surface temperature anomalies (or departures of the observed sea surface temperatures from the long-term averages) were important factors that influenced their forecasts.

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.

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, 2016, The American Meteorological Society.