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).

Advertisements




The Hurricane Center Responds to Criticisms over its Forecasting of Erika

16 09 2015

Dale C. S. Destin |

The U.S. National Hurricane Center (NHC) has responded to the criticisms over its forecasting of Tropical Storm Erika. On its official blog site called Inside the Eye, the NHC has acknowledged that the forecasting of Erika does not represent its finest hour.

Tropical Storm Erika Over the Eastern Caribbean

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

Like only consummate scientists are given to do, they candidly have accepted that the forecast errors for Erika were larger than usual and have given acceptable reasons for these. Chief among the reasons is the weak and disorganized nature of the storm.

As a member of the meteorological community, I greatly appreciate the challenges of tropical cyclone and weather forecasting. My Antiguan colleagues and I also grapple with many of the issues identified in the article and empathize with the hurricane specialists of the NHC. We also congratulate them for their many years of service of the highest order.

Regretfully though, the article did not address the “800-pound gorilla” in the room i.e. the impact of Erika on Dominica. The aim of the blog seems to be that of only explaining the errors in forecasting Erika in relation to Florida. There was no mention of what happened in the Commonwealth of Dominica and the fact that no watch or warning was issued for that island notwithstanding the country was located within the 105 miles radius extent of stated storm force winds.

Douglas-Charles Airport in the wake of Tropical Storm Erika

Douglas-Charles Airport in the wake of Tropical Storm Erika, August 2015.         Credit http://dominicanewsonline.com/

Erika rained catastrophic damage on Dominica. While there may not have been any storm winds, one of the rain-bands from Erika, sat on the island, produced peak rainfall rate in excess of 36.5 mm (1.44 in) per hour and caused a deluge almost of biblical proportion. Most of Dominica had in total over 320 mm (over 12 in) of rain in less than 12 hours, 229 mm (9 in) of which fell in 6 hours. The damage was calamitous: dozens are dead or missing, hundreds of homes destroyed or uninhabitable and over US$245 million in damage (around 50% of GDP), setting the country’s development back, at least, 20 years.

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

24-hr Radar Rainfall Estimate ending 2 am Thu, 28 Aug, 2015

Some of the questions on people’s minds are: Did the NHC contact Barbados Meteorological Service, who is responsible for issuing weather bulletins for Dominica, to discus issuing a watch or warning? If no, why not; if yes, why was nothing issued?

In the final analysis, NHC plays a consultancy role in these matters; ultimately, the responsibility rests with the responsible national meteorological service, in this case, Barbados, for whatever tropical cyclone alerts are issued or not issued for Dominica.

To be clear, let me emphasize that I am not pointing fingers at anyone. Given the tens of billions of gallons of water that fell on Dominica in a very short space of time and the rugged terrain of the country, which boast 365 rivers, it is unclear, as to whether a watch or warning would have made a significant difference. But as apart of the further review of Tropical Storm Erika, there are inherent questions that we have to address.

I would like to highly commend the NHC for its continuous and honest self-examination, which all of us in the field can benefit from. There may be such a thing as a perfect storm, but there is no such thing as a perfect forecast. We (meteorologists) do the best we can and try as much as possible to learn from our successes as well as our failures.

Here’s the link to the NHC blog titled, After Further Review: Tropical Storm Erika: https://noaanhc.wordpress.com/2015/09/10/after-further-review-tropical-storm-erika/








%d bloggers like this: