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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Record Breaking Rainfall

11 05 2012

by Dale C. S. Destin

This is the wettest start to May at the V. C. Bird International Airport, based on available record, which dates back to 1971. The rainfall for the first seven days of May, 2012 is now the most on record for all Mays with 121.9 mm or 4.80 inches; the previous highest was 63.4 mm or 2.50 inches recorded in 1990. The rainfall was caused by a persistent deep-layered trough system, which channelled a lot of moisture from South America into the area resulting in periods of rain, showers and thunderstorms. The heaviest rainfall occurred on Saturday, 5 May with 76.5 mm or 3.01 inches falling in a short period of time, about 3 hours. This resulted in minor to moderate flooding in some low-lying and flood prone areas. May 5 also had its highest total on record, and it tied with May 30, 1992 for the fourth wettest day for all Mays.

Our outlook for May calls for above normal rainfall and near normal temperature and wind. Given what has happened thus far, we could easily see this May becoming one of the top 10 wettest Mays on record. Does anyone want to guess/forecast what the final rainfall total for the month at the airport is going to be?  Here is a guide; the average and median totals for May 12 – 31 are 16.6 and 25.1 mm respectively; the max and min totals are 444.8 and 7.5 mm respectively (1981 – 2010). What is your guess/forecast total for the month? Tweet us at www.twitter.com/anumetservice or www.facebook.com/anumetservice.

Daily Rainfall Totals at the V. C. Bird International Airport – May 1 to May 7, 2012:

May 1    1.0 mm or 0.04 in

May 2    3.0 mm or 0.12 in

May 3    10.7 mm or 0.42 in

May 4    0.9 mm or 0.04 in

May 5    77.9 mm or 3.07 in

May 6    10.6 mm or 0.42 in

May 7    17.8 mm or 0.70 in





May 5, 2012 Rainfall in Perspective

6 05 2012

Yesterday, Saturday, May 5, 2012 was a very wet day across most, if not all, of Antigua. The wet and thundery weather rolled in during the morning hours, impacting the southern parts of the island first, then the northern. Because the line of weather was quite narrow, it never impacted the whole island at any given time. The wet and thundery weather was quite intense between 10 am and 1 pm, across the northern side of Antigua, during which time 77.0 millimetres (mm) or 3.03 inches of rainfall were dumped on the airport and nearby areas. This resulted in at least moderate flooding in some low-lying and flood prone areas in the northern side of the island. For full radar coverage of the whole event: http://www.youtube.com/watch?v=JZX_9eaXFvE&feature=plcp

Radar Image - May 5, 2012, 11:15am

Radar Image showing heavy rainfall across Antigua on May 5, 2012, 11:15am

It has now turned out that the rainfall for Saturday, May 5, 2012 is the highest total for that day based on available record going back to 1971 for the airport. Also, it was the first time this much rain fell in one day during the first half of the month, and it tied with May 30, 1992 for the fourth highest total for a single day in May.  Further, it is only the fifth time on record that a single day has received more rainfall, during a given year, before May 16. The previous highest total for May 5 was 23.4 mm in 1975.

Yesterday’s rainfall has brought the total for May, at the airport, to 93.5 mm or 3.68 inches. This total is above normal for the month in line with our forecast for the month.  More rainfall is anticipated during the upcoming week and with so much time left in the month. There is a high chance of May having well above normal rainfall.

 

Top 4 highest one-day totals for May, recorded at the airport (1971 – 2012):

1              178.6 mm or 7.03 inches in 1987

2              148.7 mm or 5.85 inches in 1987

3              85.6 mm or 3.37 inches in 1979

4              77.9 mm or 3.07 inches in 2012

4              77.9 mm or 3.07 inches in 1992

 

Top 5 highest one-day totals prior to May 16 for the period 1971 – 2012

1              93.9 mm or 3.70 inches in Apr 2010

2              91.7 mm or 3.61 inches in Apr 1990

3              87.6 mm or 3.45 inches in Mar 2002

4              79.3 mm or 3.12 inches in Mar 1985

5              77.9 mm or 3.07 inches in May 2012





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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