September 2016 to February 2017 Climate Outlooks for Antigua and Barbuda

29 09 2016

Dale C. S. Destin |

The September 2016 to February 2017 climate outlooks are now available for Antigua and Barbuda. Over the long-term (September-February), above to near normal rainfall is expected. However, in the short-term – September to November (SON), below to near normal rainfall is expected. The droughts are more likely than not to remain as is or end over the short-term. Meanwhile, uncomfortably warm temperatures are expected for the upcoming six months, especially during the short-term.

Drought

August 2016 is the wettest since 2011 and the wettest of any month since November 2014. It was a wetter than normal August with an island-average of 130.3 mm (5.13 in). Notwithstanding, it was not wet enough to end the droughts, which have gone past 38 months.

Looking forward – there is a moderate chance (55%) of the droughts either not getting worse or ending during the period SON. Conversely, there is also a moderate chance of the SON period having below normal rainfall. Notwithstanding, over the long run, above to near normal rainfall is expected. Thus, drought watches are in effect instead of warnings.

jun-nov2016_rainfall

The warm phase of El Nino Southern Oscillation (ENSO) – El Nino, came to an end in May. At which time, the chance of a cold phase i.e. La Nina was in excess of 75%. However, as of this month, the probability of La Nina is at 55% and declining.

If you are in our part of the world – the Caribbean, a La Nina would be more than welcome. Unlike El Nino, La Nina often brings us more than usual rainfall. Hence, given our severe water crisis of the past three years, to not have a La Nina as “promised” would be a great disappointment.

The rains over the past weeks have put a huge dent into the droughts. We are experiencing one of our wettest, if not wettest September in over 20 years. There is optimism that a few of the droughts have ended. More will be said on this, after a full assessment, by the middle of October.

Precipitation and temperature

Year-to-date, Antigua, on average, has had more than twice the amount of rainfall than for the same period last year. Notwithstanding, we are still over three inches in the “red” relative to the long-term average for January-August of 647.7 mm (25.50 in).

This up-tick in rainfall has a reasonable chance of continuing over the long-term: September 2016 to February 2017, there is an 80% probability of above to near normal rainfall. However, the projected rainfall for 2016 is 657 to 1218.5 mm (25.9-48.0 in) or below to near normal.

For the seasons SON (autumn) and DJF (winter), there are equal chances of below, near or above normal mean temperatures. However, over the long-term, mean temperatures are likely to be above normal. Higher than usual night-time low temperatures are likely to continue through November, resulting in continued uncomfortable warmer nights.

The hurricane season

We are passed the peak days of the hurricane season for us and for the season overall. However, we are still very much in the most active period of the hurricane season – August to October. Thus far, the 2016 Atlantic hurricane season has produced, 12 named storms, four hurricanes and one major hurricane.

The 12 named storms are 50% more than the average of 8 to date [September 25]. However, the accumulated energy (ACE) index which matters most, is less than 50% of the average of 106. The relatively low ACE is indicative of the fact that the storms have been generally weak.

The forecast is for a near normal season with around 15 named storms, 7 becoming hurricanes and 3 major hurricanes; this includes those already formed.

Notwithstanding the forecast, we need to be fully prepared, as it only takes one hurricane to set our life and community back by decades. Be prudent: prepare for the worst and hope for the best!

See the following links for the full outlooks: September 2016, September-November 2016, December 2016-February 2017September 2016-February 2017Drought, 2016 Updated Hurricane Season Forecast.

The next set of outlooks will be available by October 5, 2016.





Antigua and Barbuda Battered by Torrential Rains

16 09 2016

Last week Monday, Antigua and Barbuda was battered by torrential rains from a tropical disturbance. This resulted in major flooding in many parts of the country, especially in low-lying and flood-prone areas. We had not seen such downpours in nearly a decade.

Satellte loop of the tropical disturbance

Satellite loop of the tropical disturbance

Many parts of Antigua got more than the average total rainfall for September in less than 24 hours. On average, Antigua got around 139.7 mm (5.5 in) in less than 24 hours, with many areas getting over 180 mm (over 7 in), which is much more than the island-average of 144.0 mm (5.67 in) for September.

RadarRainfallAccumulation-24hrs ending 2amSep62016

Radar rainfall accumulations for the 24 hrs ending 2 a.m. Sep 6, 2016

With the average rainfall total of 139.7 falling on 108 square miles (the size of Antigua), it means that about 8.6 billion imperial gallons (IG) of water fell on Antigua between 2 am, September 5 and 2 am September 6. As a reference, this amount of water could serve the country for three years. It’s also close to 100 times the 90 million IG collected by Potworks Dam.

Clearly, with all this water, it should come as no surprise the we had areas with major flooding. Notwithstanding the negative impacts of the flooding, it was rainfall to make most Antiguans and Barbudans, particularly water resources managers and farmers, smile from ear to ear. It resulted in significant recharging of catchments, many of which were dry or below extraction levels since early last year.

Potworks Dam: left – Aug 24, 2016, right – Sep 6, 2016

Potworks Dam, which was dry for over a year, was filled to around one-eighth, according to the Antigua Public Utilities Authority – APUA (the water authority) . It collected around 90 million IG of water, enough to augment water supplies for the next three to four months. APUA has since indicated an easing of water rationing, at least, for the short-term.

Monday September 5, 2016 was the wettest day for quite a while for many areas of Antigua. At the Airport it was the wettest day since Hurricane Earl’s unwelcome visit in 2010. It was also one of the wettest days since Hurricane Lenny in 1999. Only three other days have been wetter since Lenny – the “father” of all flooding for Antigua.

Although this type of rainfall has been rare for the past 15 years, it does occur fairly frequently at a rate of around once every four to five years, based on rainfall measured at the V. C. Bird International Airport – the home of the Antigua and Barbuda Meteorological Service. In other words, it has about a 20-25% chance of happening each year.

The rains caused major flooding of low-lying and flood-prone areas. This resulted in an unknown number of cars being stalled in flood waters and a number of homes came very close to being flooded. There were minor rock slides reported but damage, if any, is unknown. In the wake of the event, many roads were damage due to erosion.

Flooded road

Flooded road

Flooded road

Flooded yard

The event proved very challenging to forecast. Several days before the event, most models forecast up to five inches of rainfall to occur. However, as we got closer to September 5, the models shifted the rainfall to the south of Antigua. Up to the morning of the event, none of the models surveyed came remotely close to forecast the rainfall that eventually occurred.  

Can we get a repeat of last week Monday?  It is probable but highly unlikely. The chance of getting two such days in a given year is around seven percent. So whereas getting dowsed by such drenching rainfall is not unusual, especially at this time of the year, it is highly unusual for it to happen twice in a year.

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