Driest June in Over a Generation for Antigua, Droughts Continue

23 07 2018

Dale C. S. Destin |

June 2018 was the driest for Antigua in 33 years – over a generation. With the median age of the Antiguan population being around 31, most Antiguans have never seen a drier June. Not since 1985 has Antigua experienced a drier start to summer.

Potworks_Dam_Jul6_2018

The total rainfall for the month of 12.7 mm (0.50 in) was a parched 18% of what normally falls – 69.3 mm (2.73 in). Thus, there was an excruciating 82% rainfall deficit for the month.

This was the third driest June on record dating back to 1928. Only 1985 and 1974 Junes were drier with 12.4 mm (0.49 in) and 8.1 mm (0.32 in) respectively. The 12.7 mm for this June has a return period of 34 years i.e. such severe dryness for the month only occurs once in every 34 years, on average.

ModerateMetDroughtUnchangedThe last three-month period – April to June, upon which the assessment of the current intensity of the drought is based, had 128.3 mm (5.05 in), only around half of the normal total of 258.6 mm (10.18 in). This puts the meteorological drought current intensity at moderate, unchanged the previous assessment.

Overall, we are in a serious meteorological drought, but currently it is at moderate intensity. The overall description of the drought is based on the worst intensity achieved since it started; however, over time, the intensity will fluctuate.

Potworks Dam, with a billion-gallon capacity, has been totally dry for a couple of months now. The vegetation of the Island is struggling – grass has virtually ceased growing in some locations. Many fields are bare, with some having large cracks. These are indicative of the fact that the droughts not just meteorological, are at moderate levels or worse.

Happily, the full impacts of the droughts continue to be masked by the presence of the desalination plants; however, impacts are starting to break through. Potable water is being rationed, some places have been left without water for many hours to weeks, at a time. There will be a big press conference this morning by APUA – the water authority, to provide answers to the water problem.

The dry season – January to June, had well below normal rainfall. On a scale of 1 to 100, with 100 being best rainfall situation and 1 being the worst, the rainfall was less than a 10. Only 254.3 mm (10.01 in) or 59% of the normal total of 434.6 mm (17.11 in) fell. It was the 10th driest dry season on record dating back to 1928. Only dry season 2015 was drier since 2004.

RainfallForPast24Months_June2018

Rainfall (in) for the past 2 yrs. All periods showing well below or below normal rainfall.

The nine-month period – October 2017 to June 2018, the duration of the drought thus far, is deemed severely dry. This means that the total is in the bottom 5% of the historical data. Such dryness happens around once every 20 years, on average.

The total for the last nine months of 464.6 mm (18.29 in) is the lowest since 2001 and the third lowest on record dating back to 1928. The period normally gets 845.1 mm (33.27 in).

Based on the last set of rainfall outlooks from regional and especially international sources, the news remains bad for rainfall. Below normal rainfall is most likely for the next six months – August 2018 to January 2019. Thus, there is every reason to believe that the droughts will continue and likely worsen. The chance of the droughts ending is at most 20% or slight.

Prob Multi-Model Ensemble Forecast For ASO_Jul2018

Probabilistic Multi-Model Ensemble Forecast of Rainfall For Aug-Oct 2018

Recall that the current drought started in October 2017 with the intensity at serious levels. On average, serious meteorological droughts last for close to a year, but not continuously at serious intensity. Will it go for another three months? Yes, it is now almost certain that this drought will last for a year or more.

Our confidence of 2018 being a drier than normal year is growing. It has increased from 60% to 75% confidence. The best forecast for the amount of rain for the year is around 855 mm (33.7 in) with a 70% chance of the amount ranging between 625 mm (24.6 in) and 1139 mm (44.8 in). Normally, we get 1206.5 mm (47.5 in) annually.

Accumulations_June2018
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Updated Hurricane Season Forecast: Near to Above Normal Season is Now Likely

17 07 2018

Dale C. S. Destin |

Good news and bad news: Our July updated forecast for the 2018 Atlantic Hurricane Season is now available and it indicates that the hurricane season will likely be near to above normal. The prediction is for an accumulated cyclone energy (ACE) index of 99, 12 named storms, 5 becoming hurricanes and 3 becoming major hurricanes.

Jul2018HurricaneSeasonOutlook

The good news is that there is a 37 percent chance of there being a near normal season. The bad news is that there is also a 37 percent chance of there being an above normal/active season; hence, the near to above normal forecast for the season.

Recall that during a near normal season, there is a 33% chance of a named storm (tropical storm or hurricane) affecting, i.e. passing within 120 miles of Antigua and Barbuda. By comparison, during an above normal season, the chance soars to 75%.

With respect to hurricanes, the chance of us being affected during a near normal season – 18 percent, more than triples – 59 percent, for an above normal/active season. Further, we have never had a major hurricane during a near normal season. Clearly, an active season is least prefered.

Chance of Anu Being Affected By TS

These new numbers represent a marginal increase above those of the previous forecast. Previously, the forecast called for an ACE of 93, 11 named storms, 5 hurricanes and 2 major hurricanes. If the season turns out to be near normal, it would be due mainly to cooler than normal sea surface temperatures, across the tropical North Atlantic. If it turns out to be active, it would be mainly due to the absence or late development of El Nino.

Recall that the ACE is the overall predictor of a hurricane season, it is a measure that represent the total number of storms, their intensities and durations.

A typical season has an ACE index of 106, 12 named storms, 6 hurricanes, and 3 major hurricanes. Major hurricanes have sustained wind speeds of at least 178 km/h or 111 miles per hour (e.g., Category 3 or higher), based on the Saffir Simpson Hurricane Wind Scale.

If this forecast pans out, 2018 would be the least active since 2015. Notwithstanding, a season with activity second only to 2017, since 2005, cannot be ruled out.

According to other forecasts surveyed, the latest consensus is for an ACE of 89, 12 named storms, 5 hurricanes and 2 major hurricanes. Thus, our forecast is calling for slightly higher activity; however, regardless of the forecast, you should always prepare well each season, as it only takes one hurricane to ruin your year.

The Atlantic hurricane season started June 1 and will continue until November 30.

We will be updating this forecast by August 10.

If you found this article informative, I would be very grateful if you would help it spread by emailing it to a friend, or sharing it on Twitter or Facebook.

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