Antigua’s Unenviable Record Worst Drought Continues

25 04 2016

Dale C. S. Destin |

Notwithstanding the significant rainfall of the past week, our unenviable record worst drought continues. However, the rains did bring some much-needed relief, as many residents got their cisterns and other catchments replenished. The precipitation also brought some relief to our farming community and landscape.

No sign of water in Potworks Dam, Antigua, April 22, 2016. Photo courtesy Karen Corbin – President of the Humane Society

No sign of water in Potworks Dam, Bethesda, Antigua; April 22, 2016. Photo courtesy Karen Corbin – President of the Humane Society

Recall that there are, at least, four types of droughts – meteorological, agricultural, hydrological and socioeconomic, which is the worst. Antigua has been in these droughts for around two months shy of three years. Of the mentioned droughts, the rains had the greatest impact on the meteorological and agricultural droughts.

For the week ending April 23, the island-average rainfall for Antigua was 63.3 mm (2.49 in). To have ended at least the meteorological drought, we needed over 100 mm (4 in); much more was need to end the other droughts.

Based on a mixture of rain gauge measurements and radar estimates, the rainfall across the island was quite variable, ranging from 25 mm (1 in) in the west to 152 mm (6 in) in the northeast. Notwithstanding, most areas got 40-100 mm (1.5-4 in).

24-hr Estimated Rainfall, From 8 pm April 17, 2016 to 8 pm April 18, 2016

24-hr Estimated Rainfall: From 8 pm April 17, 2016 to 8 pm April 18, 2016

At the V. C. Bird International Airport (VCBIA), the 42 mm that fell on April 18 makes it the wettest day since October 28, 2014. It was also the wettest April 18 at VCBIA since 1992 and 15th wettest of 1620 April days on record since 1962.

VCBIA also had a near record wet spell for April – six consecutive days with at least 1 mm (0.04 in), second only to the seven recorded in 1970. The six-day (April 17-22) total of 70.4 mm (2.77 in) at VCBIA, is now the fourth wettest for the month. With respect to a week, it’s the wettest for April since 2010 and the wettest for all weeks since October 23-29, 2014.

As of Sunday morning, April 24, the island-average rainfall for Antigua for the month was 80.5 mm (3.17 in). Thus far, this is the wettest April since 2013, when we had 132.1 mm (5.20 in). It is also our fourth wettest month since December 2014. On average, April is the fifth driest month with 85.6 mm (3.37 in).

The wet week was all due to a cold front preceded by an associated trough. Both systems have since been replaced by high pressure.

The wet weather has eased the meteorological drought to slight levels; however, not much has changed regarding the more serious hydrological and socioeconomic droughts. Follow us as we continue to monitor our rainfall closely.

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Potentially Drought-Busting Rainfall This Week

17 04 2016

Dale C. S. Destin |

A trough system could potentially cause drought-busting rainfall across Antigua and the rest of northeast Caribbean during this week. The system could dump up to 150 mm (6.0 in) of rain on the Leeward Islands and the Virgin Islands over the next six days, starting  tonight – Sunday night.

GFS forecast rainfall total for the period 2 pm, April 16 to 2 pm, April 23, 2016

GFS forecast rainfall total for the period 2 pm, April 15 to 2 pm, April 22, 2016

We could get drought-busting rainfall i.e. sufficient rainfall to bring a welcome end to the meteorological and agricultural droughts taking place across Antigua and nearby islands. However, it is unclear as to whether it will be enough to replenish surface catchments and aquifers to end the more serious socioeconomic droughts, which are costing the islands dearly. Nevertheless, the rainfall is likely to put a big dent in this drought also.

Given the potential amount of rainfall that could occur, at least moderate flooding is possible of low-lying and flood-prone areas across the northeast Caribbean, including Antigua and Barbuda. Thus, the requisite watches and warnings may be required for portions of this week.

GFS probability forecast of total rainfall for April 17-23 exceeding 75 mm (3 in)

GFS probability forecast of total rainfall for April 15-22 exceeding 75 mm (3 in)

GFS probability forecast of total rainfall for April 17-23 exceeding 150 mm (6 in)

GFS probability forecast of total rainfall for April 15-22 exceeding 150 mm (6 in)

A number of weather models, including two of the best – the Integrated Forecast System (IFS) and the Global Forecasting System (GFS), are showing very high probabilities of this week being very wet, especially relative to April. However, it is not a 100% certain. Further, the eventual rainfall total is quite uncertain.

Most for the precipitation is likely to be in the form of rain from layer-type clouds as opposed to the showers from convective-type clouds. Notwithstanding, thunderstorms are possible every day from Monday to Friday. The sun could also be hidden by thick clouds for most of the week.

The normal rainfall for April is 85.6 mm (3.37 in). On record dating back to 1928, April 1981 is the wettest with 245.4 mm (9.66 in), and the driest is April 1944 with 5.8 mm (0.23 in). At the V. C. Bird International Airport, the normal rainfall for April 17-22 is 12.7 mm (0.50 in). The wettest was 1992 with 112.0 mm (4.41 in) and the driest of 0.0 mm occurred on at least six occasions since 1961.

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The 2016 Atlantic Hurricane Season Early Forecast

15 04 2016

Dale C. S. Destin |

Early forecasts just issued for the upcoming 2016 Atlantic hurricane season (AHS) indicate a near normal season is most likely. However, relative to the past three years, this season could be much more active.

Ensemble forecast

The ensemble (mean) forecast, based on predictions from Klotzbach of Colorado State University, Saunders and Lea of Tropical Storm Risk.com (TSR) and AccuWeather.com, is for 13 named storms, 6 becoming hurricanes and 3 becoming major hurricanes.

2016_Hurricane_Season_Forecast

A better indicator of the activity for the season is the accumulated cyclone energy (ACE) index which is a measurement of the strength and duration of each tropical cyclone. Summing together the ACE of each cyclone, provides a more complete picture of how active the season is likely to be outside of just the number of storms.

This year, the ensemble forecast calls for an ACE index of 85. If this forecast pans out, the 2016 season would be around 136%, 27% and 35% more active than 2013, 2014 and 2015 respectively.

It must be noted though that there is very low skill in forecasting the AHS (June to November) in April. However, this is the best available forecast for the season, at this time, and can be used as a guide for what is possible. A more skillful forecast will be available around June 1.

End of Atlantic active phase?

Around 1995, the AHS went from a quiet to an active phase. The average annual number of named storms increased from 9 to 15. There is now increasing evidence that we have seen the end of that active phase.

If the active phase has in fact ended, it would mean a reduction in the mean number of tropical cyclones (depressions, tropical storms, hurricanes) across the Atlantic over the next 20 to 30 years. This would translate to an annually reduced probability (chance) of us being impacted by a tropical cyclone between now and around the year 2041.

The x factors

There are at least two climate factors that could cause the hurricane season to be quieter than is currently being predicted. El Nino is ongoing and is virtually synonymous with inactive AHSs. The forecast is for a transition from El Nino to neutral conditions around the middle of the year and possible La Nina around October. However, if El Nino were to persist beyond summer, we would see another quiet hurricane season. On the other hand, La Nina could lead to an active season.

The second potential inhibitor of the 2016 AHS is the transport of cooler-than-normal sea-surface-temperatures (SSTs) into the tropical North Atlantic by ocean currents originating south of Greenland. Reduced SSTs hinder tropical cyclone formation and growth.

Probability of Antigua being hit by a hurricane

According to Klotzbach, the likely best similar years to the upcoming 2016 AHS are 1941, 1973, 1983, 1992, 1998 and 2014. Of these years, we were hit by Hurricane Georges and Tropical Storm Bonnie in 1998 and Tropical Storm Christine in 1973. Thus, based ONLY on similar years, the probability of Antigua being hit this year by one or more named storms is around 39%, while the probability of one or more hurricanes is around 15%.

In general, the probability of Antigua being hit by one or more named storms annually appears to vary according to the phase of the Atlantic. During the quiet phase of 1962 to 1994, the probability of one or more named storms was around 26%, while the probability of one or more hurricanes was around 14%. Meanwhile, for the active phase of 1995 to present, the probability of one or more named storms increased to around 55%, while the probability of one or more hurricanes is around 35%.

Based on the climatological period of 1981-2010, the probability of being hit by one or more named storms is around 41%, while the probability of one or more hurricanes is around 28%.

2015 hurricane season and lessons learnt

The 2015 AHS was quiet; it produced 11 named storms, 4 hurricanes and 2 major hurricanes. The ACE index total was 63, the fourth lowest since 1995. Notwithstanding it being a quiet year, Antigua was affected by Tropical Storms Danny and Erika. Damage was minor; however, closure of the country for around 24-hours, due to threat from Erika, caused an unknown loss of revenue.

Erika serves as a perfect reminder of the fact that flooding is a hazard associated with tropical cyclones. The system caused catastrophic flash floods across parts of Dominica, killing dozens of people. I our part of the world, we tend to focus a bit too much on the wind hazard associated with these systems.

Another lesson learnt was that it only takes one named storm to make it an active or miserable hurricane season for us. Thus, quiet season or not, the same hurricane season preparations are required each year.

Follow us and stay updated on the 2016 AHS via our social media platform, which includes twitter, facebook, wordpress, instagram, tumblr, and google+. Follow us also for all things weather and climate.





April to September 2016 Climate Outlooks for Antigua

1 04 2016

Dale C. S. Destin |

The latest climate outlooks are now available for Antigua. Unhappily, the news remains bleak. Below normal rainfall and above normal temperature are expected/likely for the upcoming six months – April-September 2016.

Drought

Antigua remains in drought, which has been ongoing for a record 33 months, based on record dating back to 1928.

Currently, a moderate drought or worse is evolving over the periods – January to June 2016, November 2015 to July 2016 and October 2015 to September 2016. All three periods are likely to see below normal rainfall. Drought warnings remain in place and will likely continue through the third quarter of the year.

https://anumetservice.files.wordpress.com/2016/04/jan-junrainfall2.png

The best rainfall forecast for Jan-Jun is around 271.8 mm (10.7 in); however, there is a 70% chance of it ranging between 152.7-443.6 mm  (6.0 to 17.5 in)

It is expected that El Nino will transition to a neutral state around the middle of the year and possibly to La Nina in the last third. La Nina, unlike El Nino, generally encourages rainfall across our area mainly during the wet season. Thus, there is light at the end of the tunnel but, at the moment, it’s a bit distant.

Precipitation and Temperature

Over the upcoming three months – April to June, near normal rainfall could ease the drought; however, an end to it is not anticipated.

Meanwhile, July to September is expected to see below normal rainfall. Thus, even if the drought eases during April to June, the following three months will see it reintensifying.

In the short-term, there are hopes of this dry season (January-June) being wetter than last year’s; however, it is likely to be drier than usual when compared to 1981-2010 average.

All forecast timescales (April, April-June, July-September, April-September) are likely/expected to have warmer than normal temperatures.

See the following links for the outlooks: April 2016, April-June 2016, July-September 2016, April-September 2016, Drought.

The next set of outlooks will be available by May 3, 2016.








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