The Heart of the Hurricane Season

28 08 2012

By Dale C. S. Destin

Every year, persons across the Caribbean, Central America and the US Gulf and Atlantic Coasts pray for this period to pass quickly with out a hit – the heart of the hurricane season, which covers the period August to October (ASO). For the period 1851 to 2011, Antigua has had 93 named storms and 44 hurricane giving and average per year of 0.6 named storm and 0.2 hurricane for ASO. For Antigua, the heart of the hurricane season is August to September, which accounts for 79% (Aug 34%, Sep 45%) of all storms to affect the island. (http://www.antiguamet.com/Climate/climate_anu_cyclonesbyday.html ). This period has had 83 named storms and 41 hurricane for an average per year of 0.5 hurricane and 0.2 hurricane i.e. one storm every other year and one hurricane every five years.

August 21 and September 3 are very peculiar days for Antigua. These are the two peak days for Antigua for the hurricane season with a record of 7 named storms each to have affected the island on those days from 1851 to 2011. September 3 has produced three hurricanes and August 21 has produced four. (http://www.antiguamet.com/Climate/climate_anu_cyclonesbyday.html ) Two notorious tropical cyclones that have struck on August 21 were Category 3 Unnamed Hurricane of 1871 and Category 3 Hurricane Baker of 1950.

On average, ASO has 8 named storms and 5 hurricanes per year. Historically the period has had 1237 named storms of which 806 became hurricanes – 1851 to 2011 – with August contributing 362 named storms and 230 hurricanes; 80% of all storms (Aug  23%, Sep 37%, Oct 20%) form during the period ASO. This year has been no ordinary year contrary to initial forecasts; so far for August, there have been six named storms and three hurricanes, when the month averages two named storms and one hurricane. The record for named storms for August is eight, observed in 2004. The forecast for the overall season has moved from near – below normal to above normal/active season with a consensus of 14 named storms, 6 hurricanes and 3 becoming major hurricanes; already there has been 10 named storms  and 4 hurricanes. (http://www.antiguamet.com/Climate/HURRICANE_SEASON_FORECAST/2012AtlanticHurricaneSeasonForecastAug28.pdf) looks like we will actually see more than 14 when the season ends November 30. Currently, ENSO Positive conditions (El Nino) is trying to squelch of shut down the hurricane season as is the norm; however, the tropical North Atlantic is warming and other factors such as negative North Atlantic Oscillation (NOA) and Arctic Oscillation are in favour of further warming. Of course, there are other factors to consider but these are some of the main drivers of the hurricane season. What do you think will happen? How many more named storms will we see before the season ends?

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THE ATLANTIC HURRICANE SEASON FORECAST – 2012

1 06 2012

By Dale C. S. Destin

Overview

The general consensus among tropical cyclone experts is for a near normal Atlantic Hurricane Season for 2012. The consensus forecast calls for 12 named storms, 6 hurricanes and 2 major hurricanes. A normal season averages of 11 named storms, 6 hurricanes and 3 major hurricanes (See table 1).  The science behind the outlook is rooted in the analysis and prediction of current and future global climate patterns as compared to previous seasons with similar conditions. For this season, the experts are citing a neutral to possibly warm Pacific Ocean (possibly an El Nino) and a neutral to cool Atlantic Ocean as the reason for a near normal season prediction. A warm Pacific Ocean causes hostile upper level atmospheric conditions for tropical cyclones and a cool Atlantic Ocean reduces the energy available for cyclone formation and also causes hostile atmospheric conditions for tropical cyclones (above normal trade winds, surface pressure and vertical wind shear).

Forecast (Groups) Source Forecast Date Named Storm Hurricane Major Hurricane
NOAA May 24, 2012 9 – 15 4 – 8 1 – 3
CSU Jun 1, 2012 13* 5 2
Apr 4, 2012 10 4 2
TSR May 23, 2012 13 6 3
Apr 12, 2012 13 6 3
UKMO May 24, 2012 7 – 13
NCSU 2012 7 – 10 4 – 7 1 – 3
Consensus^ Jun 1, 2012 12 6 2
61-yr Antigua Climatology1 1950 – 2010 0.7 0.4 0.2
61-yr Atlantic Climatology 1950 – 2010 10.9 6.2 2.7
30-yr Atlantic Climatology 1981 – 2010 12.1 6.4 2.7
Table 1: The Atlantic Hurricane Season Forecast – 2012. ^The Consensus forecast is themean of the June and May forecasts issued by the various groups. The Season averages (1950 – 2010): 10.9 named storms, including 6.2 hurricanes of which 2.7 intense hurricanes. 1Storms passing within 105 nautical miles of Antigua. NOAA – National Oceanic Atmospheric Administration. CSU – Colorado State University.  TSR – Tropical Storm Risk. UKMO – United Kingdom Met Office. NCSU – North Carolina State University. Consensus – The average of all the forecasts by the Met Service. *Includes the two pre-season storms – Alberto and Beryl; for the remainder of season 11 storms are predicted.

What does this mean for Antigua and Barbuda?

 Although there have been great advancements in the science of tropical cyclone (depression, tropical storm and hurricane), the science has not yet reached the stage where accurate predictions can be made of how many cyclones will form in a given year. Also, the science cannot accurately predict when and where these systems will move or make landfall months in advance. The details of the large-scale weather patterns that direct the path of these cyclones cannot be predicted more than a few days into the future.

There is no clear correlation between the number of tropical cyclone in the Atlantic yearly and the number that affects Antigua and Barbuda. As well, there is no detected trend in the percentages of Atlantic Tropical Cyclones that reach our islands yearly. However, for a near normal season, the climatology (1950 – 2010) suggests the following for Antigua and Barbuda (the 95% confidence interval in bracket):

  • 58% probability or (41 to 74%) probability of at least one named storm
  • 32% probability or (19 to 50%) probability of at least one hurricane
  • 19% probability or (9 to 36%) probability of more than one named storm
  • 10% probability or (3 to 25%) probability of more than one hurricane
  • 0 – 3 named storms, including:
  • 0 – 2 hurricanes

Over all, there is a 46% (33 to 59%) probability of at least one named storm per season, 28% (17 to 41%) probability of at least one hurricane, 16% (8 to 28%) probability of more than one named storm and an 8% (3 to 18%) probability of more than one hurricane. The most likely months for tropical cyclones to affect Antigua and Barbuda are August and September. Of all cyclones to impact Antigua, 79% (63 to 90%) occurs over the period August – September. For a near normal season, this number decreases slightly to 73% (54 to 86%) with the average impact date of August 30 (± 20 days). By climatology, at least one named storm impacts Antigua and Barbuda every two to three years on average and at least one hurricane every two to six years. See graph 1 below for a distribution of Antiguan Tropical Cyclones for the period 1851 to 2011.

The 2011 Hurricane Season

The 2011 Atlantic Hurricane Season produced nineteen (19) named storms. Of the nineteen (19) storms, seven (7) became hurricanes and four (4) strengthened to achieve major hurricane status (category three (3) or higher on the Saffir-Simpson Hurricane Wind Scale). The strongest tropical cyclone was Major Hurricane Ophelia with peak winds of 140 mph, category 4. By the national definition, Irene and Maria hit Antigua and Barbuda, Ophelia hit Barbuda and brushed Antigua; all were tropical storms at the time of affecting the area. Damages to the islands were minor. The season was well above normal (extremely active) with respect to named storms and near normal in terms of hurricanes. Further, the season was above normal in terms of major hurricanes and Accumulated Cyclone Energy (ACE) index. This season tied with the 2010 and 1995 for the second highest number of named storms for the period 1944 to 2011 and tied with 2010, 1995 and 1887 for the third highest since record began in 1851. The above normal season was attributed primarily to above normal sea surface temperature in the Atlantic and the lingering effects of a La Nina Episode.

It Only Takes One

Regardless of the numbers, we should always approach the hurricane season in the same manner each year: be aware and be prepared. The prevention of the loss of life and property from tropical cyclones is a responsibility that should be shared by all. As a reminder, recall our lesson from Hurricane George of 1998: it only takes one hurricane to make it a bad season. Further, Hurricanes Jose and Lenny impacted us during a near normal season – 1999; thus, we cannot be complacent because the forecast calls for a near normal season.

Accordingly, the Meteorological Service will play its usual role in alerting the public of any tropical cyclone that may form and threaten Antigua and Barbuda, the Leeward Islands and the British Virgin Islands. We endeavour to provide weather and climate information for the protect life, property, livelihood and the enhancement of the economy. Although the hurricane season officially runs from June 1 through November 30 each year, tropical cyclones can and have occurred outside the season – be prepared!

For more information see the links below or email me at dale_destin@yahoo.com. You are also welcome to follow us via twitter facebook youtube and blog . Click here for pdf format

References

Colorado State University, Fort Collins, 2012 Atlantic Season Hurricane Forecast [online]<http://hurricane.atmos.colostate.edu/forecasts/2012/june2012/jun2012.pdf>%5BAccessed 1 June, 2012]

National Oceanic and Atmospheric Administration, Silver Spring, NOAA 2012 Atlantic Hurricane Season Outlook [online].              Available from: <http://www.cpc.ncep.noaa.gov/products/outlooks/hurricane.shtml> %5BAccessed 24 May, 2012]

North Carolina State University, Raleigh, 2012 Atlantic Tropical Cyclone Outlook [online]. Available from: <http://cfdl.meas.ncsu.edu/research/TCoutlook_2012.html>%5BAccessed 24 May, 2012]

Tropical Storm Risk, London, Pre-Season Forecast for Atlantic Hurricane Activity in 2012 [online]. Available from: <http://www.tropicalstormrisk.com/docs/TSRATLPreSeason2012.pdf>[Accessed 24 May, 2012]

United Kingdom Met Office, Exeter, Seasonal Forecasting of Storms [online]. Available from: <http://www.metoffice.gov.uk/weather/tropicalcyclone/seasonal/forecasting-method>%5BAccessed 24 May, 2012]





Record Number of Storms for May 2012…Could Antigua be affected?

29 05 2012

By Dale C. S. Destin

It seems like someone has forgotten to tell the Atlantic the forecast. All forecasts to date are indicating a near normal Atlantic Hurricane Season. The Atlantic Hurricane Season runs from June 1 to November 30. Notwithstanding, the second pre-season storm – Beryl – for May and the year has formed (May 26 to present). This tied with May of 1887 for the most named storms (2) in May for a given year based on record, which goes back to 1851. The other pre-season storm was Alberto – May 19-22. Although Beryl poses no threat to Antigua, many years ago two pre-season hurricanes affected the area.

All forecasts to date for the Atlantic Hurricane season call for 7 to 15 named storms – a near normal season. The near normal forecasts are due primarily to near normal sea surface temperatures across the Equatorial Tropical Pacific Ocean and normal to below normal sea surface temperatures across the North Atlantic Ocean, particularly the Tropical North Atlantic. However, although there have never been two storms in the same year in the month of May, past pre-season storms have not portend anything about the activity of the upcoming season. Of the past five seasons with pre-season storms or hurricanes, two were above normal, two were near normal and one was below normal. Of course we have never seen two tropical storms in may; let’s see how the year turns out.

Although pre-season storms do not happen often, they are not unusual in the Atlantic Basin (Atlantic Ocean, Caribbean Seas and the Gulf of Mexico). The currently define Atlantic Hurricane Season, June 1 – Nov 30, accounts for about 97% of all Atlantic tropical cyclones (storms and hurricanes); of the remaining 3%, 48% occurs in May and the other months account for the rest.  Further, of the pre-season tropical cyclones, 80% occurs in May (See table 1). Off season tropical cyclones are most likely to occur in the Central to Western Atlantic Ocean and most do not make landfall. Of the tropical cyclones that did strike land, most have affected areas surrounding the Caribbean Sea. Cumulatively, these pre-season cyclones have caused the death of hundreds primarily in Hispaniola and Cuba. The strongest pre-season (and post-season) tropical cyclone was Hurricane Able in May 1951.

Antigua has been struck at least twice by pre-season tropical cyclones. The island was impacted by Hurricane Alice2  January 2 – 3, 1955. The system formed on December 30, 1954 and continued until January 6, 1955; this is the only Hurricane and the first of only two tropical cyclones to span two calendar years; the other tropical cyclone was Tropical Storm Zeta of 2005-2006. Previous to 1955, the island was impacted by (Unnamed) Hurricane One of 1908 March 7 – 8. The system formed on March 6 and dissipated March 9. Both hurricanes passed within 75 statute miles northwest of Antigua and also affected most of the rest of the Northeast Caribbean as the travelled from northeast to southwest. Both also dissipated in the Eastern Caribbean Sea near the islands (See Map 1 and 2)

The record shows that at least one tropical cyclone has occurred in every month of the year. Antigua has been affected by tropical cyclones in seven of twelve months of the year – January, March, July, August, September, October and November. For all of us in this part of the world, a certain level of preparedness is required even outside the hurricane season.

Map 1: Partial Plot of the 1954 Atlantic Hurricane Season. Tropical Cyclone Number 11 is Hurricane Alice2, which affected Antigua and the NE Caribbean in early January 1955.

Map 1: Partial Plot of the 1954 Atlantic Hurricane Season. Tropical Cyclone Number 11 is Hurricane Alice2, which affected Antigua and the NE Caribbean in early January 1955. Adapted from wikipedia.com

Map 2: Partial Plot of the 1908 Atlantic Hurricane Season. Tropical cyclone number one is Hurricane One, which affected the NE Caribbean in March 1908.

Map 2: Partial Plot of the 1908 Atlantic Hurricane Season. Tropical cyclone number one is Hurricane One, which affected the NE Caribbean in March 1908. Adapted from wikipedia.com

Total and Average Number of Tropical Storms by Month
(1851-2011)
Month Tropical Storms Hurricanes Antigua
Tropical Storms Hurricanes
Total Average Total Average Total Average Total Average
JANUARY 2 * 1 * 1 * 1 *
FEBRUARY 1 * 1 * 0 * 0 *
MARCH 1 * 1 * 1 * 1 *
APRIL 1 * 0 * 0 * 0 *
MAY 18 0.1 4 * 0 * 0 *
JUNE 82 0.5 32 0.2 0 * 0 *
JULY 113 0.7 54 0.3 6 * 1 *
AUGUST 362 2.2 230 1.4 36 0.2 18 0.1
SEPTEMBER 556 3.5 384 2.4 47 0.3 23 0.1
OCTOBER 319 2.0 192 1.2 10 0.1 3 *
NOVEMBER 87 0.5 58 0.4 4 * 1 *
DECEMBER 17 0.1 6 * 0 * 0 *
YEAR 1559 9.6 964 6.0 105 0.6 48 0.2
Table 1: *Less than 0.05%. The list excludes subtropical storms. Antigua
Storms and Hurricanes are those that passed within 120 statute of the
island. Data (first 4 columns) from http://www.aoml.noaa.gov








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