The Driest Year for Antigua since at Least 1871

21 12 2015

Dale C. S. Destin |

Earlier this year, we indicated that Antigua could see its driest year on record. Regrettably, this is coming to past. The country is on its way to having the driest year on record dating back to at least 1871 or 145 years ago.

Up to the end of November, the rainfall total stood at 525.8 mm (20.70 in). Based on measured rainfall, it’s the lowest on record for any January-November period dating back to 1928. Further, based on statistical analyses, we are almost 100% certain that this is the driest such 11 months since 1871.

Annual Rainfall for Antigua. Blue line - rainfall; heavy grey line - normal rainfall using base period 1981-2010

Annual Rainfall for Antigua. Blue line – rainfall; heavy grey line – normal rainfall using the base period 1981-2010.

It would take perhaps a miraculous deluge to prevent the 1983 record (681.5 mm or 26.83 in) from being broken. Over six inches of rain is required in December to prevent the record from being broken. Thus far for the month, the rainfall total is less than an inch.

There have been only 11 times in 88 years when the rainfall for December has exceeded 155.7 mm (6.13 in) – the amount required to prevent the record from falling. The probability of this happening is around 12%, El Nino or not. Currently, we are at least 70% certain that this rainfall will not materialize.

We could also see our record driest wet season (July-December). Statistically, there is a very low chance of this happening – around 8%; however, given the near record low rainfall for the month thus far, the chance is increasing.

We do not actually have data from our current stations going back beyond 1928. However, with the use of regression analysis, we were able to use other datasets to successfully extend our record back to 1871. So we now have very high quality datasets of annual and some seasonal rainfall totals dating back 145 years.

Like Antigua, most of the eastern half of the Caribbean could also see record-breaking low rainfall for 2015.

Caribbean Rainfall - Dec 2014 to Nov 2015

Nov 2014-Dec 2015 SPI. The darker the reds, the drier the weather; the darker the blues, the wetter the weather. Record or near record low rainfall for much of the eastern half of the Caribbean basin.

El Nino, Saharan dust and a positive North Atlantic Oscillation are the main culprits for the parched weather conditions for this year.

Keep following this “space” for more insights into the rainfall for Antigua and the Caribbean. Unfortunately, we have additional undesirable statistics to share with you on this subject.

Advertisements




A Memorable Below Average Hurricane Season

18 12 2015

Dale C. S. Destin |

The 2015 hurricane season came to a quiet end November 30. Overall, it was a below average year, based on NOAA’s criteria. However, for us in the Caribbean, it will live on in everlasting memory, due to the catastrophic impact of Erika on Dominica.

Tropical Storm Erika Over the Eastern Caribbean

Tropical Storm Erika Over the Eastern Caribbean Aug 27, 2015. Credit NASA

Before Erika, Danny “scare the living daylights” out of many when it rapidly and unexpectedly intensified into a major hurricane, less than 800 miles east of the Caribbean. However, as predicted, it just about died before reaching the islands.

Less than three after Danny, Erika caused horror across Dominica. In less than 12 hours, the storm deluged much of Dominica with over 320 mm (12 in) of rain, 229 mm (9 in) of which fell in less than 6 hours. Peak rain rate in excess of 36.5 mm (1.44 in) were observed leading to catastrophic flooding and mudslides.

24-hr Radar Rainfall Estimates ending 2 am Sun, 28 Aug, 2015

24-hr Radar Rainfall Estimates ending 2 am Sun, 28 Aug, 2015. Rainfall over Dominica is off the chart. At most, southwest Antigua had 30 mm (1.18 in)

There were villages flattened, around 890 homes were destroyed or left uninhabitable while about 14,300 people were left homeless. Erika killed at least 31 persons in Dominica, the deadliest disaster in the country’s history since Hurricane David in 1979.

Flood water in Dominica from Tropical Storm Erika - Aug 27, 2015

Cars being washed away in flood waters in Dominica from Tropical Storm Erika – Aug 27, 2015

The system caused around half a billion dollars in damage to Dominica, around 100% of GDP, setting the country’s development back by at least 20 years.

Erika also caused major flooding and landslides in Puerto Rico and Hispaniola. She also took the lives of five persons in Haiti.

Jun-Nov 2015 Standard Precipitation Index. Reds indicate low rainfall, blue indicate high rainfall

Jun-Nov 2015 Standardized Precipitation Index (SPI). The darker the reds (negative values), the drier the weather; the darker the blues (positive values), the wetter the weather. Most of the Caribbean basin, has had near record or record low rainfall (red), this is at least a 1 in 40 year event.

This hurricane season will also be remembered for being the record driest or among the driest ever on record for much of the Caribbean basin. Antigua, for example, had record low rainfall for the season; the rainfall was 48% below normal. Much of the rest of the region had at least 25% less rainfall than normal.

The season produced 11 named storms. Of the 11, 4 became hurricanes and 2 reached major hurricane status – category three (3) or higher. The strongest was Joaquin which had peak winds of 155 mph. The total ACE was 63% of the median or 56% of average (1981 – 2010). This is the fourth lowest since 1995.

2015_HurricaneSeasonSummary

Our ensemble forecast did quite well in predicting the eventual outcome of the season. It called for nine named storms (we got 11) of which four were predicted to become hurricanes (we got four) and one to become a major hurricane (we got two). We also predicted an ACE of 52 and we got 59.

The below average season was due largely to suppressing effect of El Nino on rainfall processes over the tropical Atlantic and Caribbean basin. Secondarily, a positive North Atlantic Oscillation caused cooler than normal sea surface temperature during the early part of the season.

Other notable facts of the 2015 Atlantic hurricane season are:

  • Combined, 2013-2015 totals 12 hurricanes. This is the lowest three-year figure since 1992-1994 (11 hurricanes).
  • The total number of major hurricanes for the period 2013-2015 is four. No other three-year interval has had fewer major hurricanes since 1992-1994 (2 major hurricanes).
  • Joaquin is the first Category 4-5 hurricane to impact the Bahamas during October since 1866.
  • The ACE for September was only 11. The Atlantic three-year (2013-2015) summed ACE for September was only 44, the lowest since 1912-1914 when only an ACE of 29 was recorded during September.
  • June-October-averaged 40,000-5,000 feet vertical wind shear (hostile to tropical cyclone) in the Caribbean (10-20°N, 90-60°W) was 28.5 knots (33 mph), the strongest on record since 1979.
  • Hurricane Fred is the farthest east that a hurricane has ever formed in the Atlantic basin.

This season reminded us all of the need to be prepared for every hurricane season, below average or not. Again, a below average season does not mean you are guaranteed a cyclone-free year. The past two years have had below normal activity, yet the region had major damage from Erika and Gonzalo (2014).








%d bloggers like this: