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]

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The Forecast for 2012 Atlantic Hurricane Season

4 05 2012

Thus far for the year, there have been two forecasts for the North Atlantic Hurricane Season, and both have predicted below normal activity. However, when one looks at the actual forecasts, it could easily be argued that these forecasts are really predicting near normal conditions. Here are the numbers for both forecasts:

                                    Klotzbach and Gray       Saunders and Lea

                             (Colorado State University)     (Tropical Storm Risk)

Named Storms          10 (12)                                            13 (11)

Hurricanes                  4 (6)                                                  6 (6)

Major Hurricanes      2 (2)                                                  3 (3)

The numbers without brackets are the forecast values, and the numbers in brackets are the normal or average values for the season, depending on the base period. The bracketed numbers differ because of the different in base period. From their numbers, I would say near normal conditions are being predicted since this is a climatological Statistical forecast, and in climatology near normal is any value that falls within the middle tercile or 33.3% of the historical data. In this case, near normal would be the range 9 to 12 named storms, 5 to 7 hurricanes, 2 to 3 major hurricanes. Saunders and Lea’s forecast is actually forecasting above normal named storms.

Persons should not put too much confidence in these forecasts thought, as historically, the ability to produce an accurate forecast for the Atlantic Hurricane Season from April lead time is very low. In other words, the Meteorological Community has very little skill in producing an accurate forecast for the hurricane season from this early in the year; these April forecasts are often wrong. See the skills graph below:

Image

December and April’s forecasts show very little to negative skill

The figure above displays the recent 10-year (2002-2011) skill for the forecast number of North Atlantic Hurricanes issued by different organisations.  The forecast precision is assessed using the Mean Square Skill Score (MSSS), which is the percentage improvement in mean square error over a climatological forecast. Positive skill indicates that the model performs better than a climatology forecast (what obtains on average), whilst a negative skill indicates that it performs worse than climatology. Two different climatologies are used: a fixed 50-year (1950-1999) climatology and a running prior 10-year climate norm. The figure compares the forecast skill of the TSR (Tropical Storm Risk), NOAA (National Oceanic and Atmospheric Administration) and CSU (Colorado State University) seasonal hurricane outlooks 2002-2011 as a function of lead time. NOAA does not release seasonal outlooks before late May. It is clear there is little skill in forecasting the upcoming number of Atlantic hurricanes from the prior December and April. Skill climbs slowly as the hurricane season approaches. Moderate skill levels are reached by early June and good skill levels are achieved from early August.

Regardless to the forecast number of named storms and hurricanes, we should always prepare the same for every season as it only takes one hurricane to make it an active season for you and ruin your year. We have recent examples of near normal seasons being quite deadly and costly. Recall in 1992, there were 7 named storms, 4 hurricanes and 1 major hurricane – Andrew. Andrew hit the United States and at the time was the costliest hurricane causing US$26 billion dollars and killing 65 persons. Closer to home, in 1989, there were 11 named storms, 7 hurricanes and 2 major hurricanes, one of which was Hurricane Hugo. Many persons remember Hurricane Hugo; this system absolutely flattened Montserrat; it left in its wake 11 deaths, 3000 homeless  and damage of about EC$1 billion. Hugo also caused significant damage to Antigua costing about EC$200 million.

References

Colorado State University, Fort Collins, Extended Range Forecast of Atlantic Seasonal Hurricane Activity and Landfall Strike Probability for 2012  [online]. Available from: <http://hurricane.atmos.colostate.edu/forecasts/2012/apr2012/apr2012.pdf> [Accessed 26 Apr 2012].

Texas A&M University, Corpus Christi, Montserrat: Emergency Planning, Response and Recovery Related to Hurricane Hugo [online]. Available from: <http://msld.tamu.edu/hrrc/Publications/researchreports/Downloads/91-02R%2BBerke%2Band%2BWenger%2BMontserrat%2B-%2BEmergency%2BPlanning%2BResponse%2Band%2BRecovery%2BRelated%2Bto%2BHurricane%2BHugo.pdf> [Accessed 24 April 2012].

Tropical Storms Risk, London, Silver Spring, April Forecast Update for Atlantic Hurricane Activity in 2012 [online]. <http://www.tropicalstormrisk.com/docs/TSRATLForecastApr2012.pdf>[Accessed 26 Apr 2012].








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