Once in a Generation Dry March for Antigua!*

30 03 2015

Dale C. S. Destin |

We are about to exit a severely dry March for most of Antigua. So far for the month, the Met Office, located at the V. C. Bird International Airport, has measured only 8.4 mm of rainfall. This severe dryness only happens once in a generation, on average. This total is not expected to change much between now tomorrow, when the month ends. Hence, this is likely to be among the top five driest Marches and the top 10 driest month of all times.

Top 4 Driest Marches for Coolidge, Antigua
March 2015 in perspective

Barring unexpected appreciable rainfall over the next 24 hours, this will be the fourth driest March on record dating back to 1928. Only March 1999, 1944 and 1930 have been drier.

Relative to other months, this March ranks 10th of all 1047 months of recorded rainfall, at the Airport, for the period.

The probability of March having such little rainfall is quite low; it’s around 3%. This means that this severe dryness we have experienced only happens once in every 33 Marches or once in a generation, on average.

Looking at the year on a whole, this is a 17 year event. The probability of a (any) month of a year, at the Airport, yielding 8.4 mm or less is around 6%. This means that this happens once every 17 years, on average.

March is the second driest month at the Airport with an average rainfall of 46 mm (1.81 in). The minimum and maximum rainfall totals on record are zero and 179.1 mm (7.05 in) respectively.

Drought

Currently, we are in our worse drought, in terms of intensity, since 2002/2003 and it is likely to get worse. We have been in a drought since September 2013.

It reached serious levels in 2014 but was reduced to slight levels in October 2014. At the end of January 2015 it had reintensified to moderate levels and with this month being brutally dry, it is set to drop to severe levels.

Projections

However, seasonal forecasters are not optimistic about rainfall for much of the rest of 2015. Indications are that El Nino, which tends to restrict our rainfall, mainly in the rainy season, is expected to continue deep into the year.

Additionally, the tropical North Atlantic sea surface temperatures are projected to remain near normal for much of the rest of the year. This is generally not helpful for rainfall in our nook of the world.

If El Nino strengthens to moderate levels or worse, our rainfall deficits are likely to be worse that those of last year’s. Recall that last year that we had a water crisis which are yet to get over.

Further, strategies and tools are required to sustainably deal with our water insecurity issues. Two such required tools are an integrated water resource management programme and an integrated drought management programme. Meanwhile, be conservative and efficient with your water usage.

[*It turned out that unexpected heavy downpours stopped March from having “once in a generation” dryness. The heavy downpours that stopped this March from being the fourth driest occurred after midnight on March 31. However, In meteorology, the last day of a month ends at 8 am on the first day of the next month. .

So, instead, the eventual total rainfall for March, at the Airport, was 11.9 mm, the driest since 2001, the seventh driest March and the 18th driest month on record. This kind of dryness, instead, happens once in every 16 years, on average]





More Drought Quenching Rainfall for Antigua

17 12 2014

Dale C. S. Destin |

Surface chart showing stationary front across northern Caribbean (red & blue)

Surface chart showing stationary front across northern Caribbean (red & blue)

More drought quenching rainfall fell today across Antigua yesterday December 16. A near stationary front (shown below on the surface chart) showered the island with much needed water. At the V. C. Bird International Airport (VCBIA), 10.9 mm of rain was measured, all falling between 2:45 pm and 6:45 pm. However, estimates from weather radar (shown below) indicate that as much as 50 mm may have fallen on northern side of the island. Over in Barbuda, a drenching 150 mm or more fell according to radar estimates. Going by what was actually measured by raingauge, at the VCBIA, the rainfall total now stands at 69.7 mm (2.74 in). This means that the Airport, thus far, has received near normal rainfall for December. However, above normal rainfall, above 91.4 mm (3.6 in) is forecast for the month. Thus, further quenching of the drought is anticipated.

Radar rainfall estimates

Radar rainfall estimates

The front did not just affect Antigua; satellite photo and TRMM data below show the cloud and rainfall signature patterns of the system stretching across much of the northern Caribbean from the Leeward Islands west to Jamaica and parts of Cuba.

 

Satellite picture of the stationary front

Satellite picture of the stationary front

Here are the rainfall totals reported by some of the other affected islands:

  • Robert L. Bradshaw International Airport, St. Kitts – 39 mm
  • Luis Muñoz Marín International Airport, Puerto Rico – 101 mm
  • Sangster International Airport, Jamaica – 38 mm
TRMM rainfall estimates

TRMM rainfall estimates

Rainfall at the VCBIA continues to run above normal for December. Exceeding 100 mm is a real possibility. If this were to happen, it would be the fourth time in the last five years. Continue to think rain.

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A Slow Start to October’s Rainfall for Antigua

20 10 2014

Dale C. S. Destin |

Rainfall continues to be a very scarce commodity in Antigua and Barbuda. Like most of the rest of the months for the past year, the rainfall for October has been quite discouraging, thus far. The first half of October has seen a significant rainfall deficit across much of Antigua according to preliminary statistics at the Antigua and Barbuda Met Service Climate Section.

Figures up to October 16 show there has been 36.0 mm of rain at the Met Office located at the V. C. Bird International Airport. This is only 50% of the October average of 71.8 mm, just about the amount that should have fallen by this point.

Rainfall_OctoberThis makes this first half of October the 16th driest at the Airport based on available records dating back to 1967. Three of the last four first half of October has seen worse rainfall deficits. However, the overall trend is positive although not significant.

Many persons were hoping that Hurricane Gonzalo would have put a dent in the drought; however, this was just not to be. The system produced only 1-5 inches across Antigua and 4-6 inches across Barbuda; however the higher totals were isolated and away from the most of the islands catchments.

The low rainfall figures appear to be due largely to sinking air associated with the Madden-Julian Oscillation in our part of the world for much of the first 16 days of October.

Of course, while these figures are interesting, they don’t tell us where the month will end up overall. A few days of wet weather, which looks unlikely at the moment, could drastically alter the statistics. So we’ll have to wait for the full-month figures before making any judgements. September had a much worse start and was able to limp into the near normal range in the end. It should be noted the rainfall for the second half of October is trending downward, although not significantly.

The outlook for the month called for near normal rainfall; thus we shall see what happens at the end of the month.

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The Sixth Driest Start to September

20 09 2014

Dale C. S. Destin |

After encouraging rainfall for August, September has been quite disappointing, thus far. The first half of September has been severely dry across much of Antigua according to preliminary statistics at the Antigua and Barbuda Met Service.

Figures up to September 15 show there has been 16.3 mm of rain at the Met Office located at the V. C. Bird International Airport. This is only 12.4% of the September average of 131.6 mm. We would expect about 57% or 74.6 mm of the month’s rainfall to have fallen by this point.

 

SixDriestFirstHalfOfSeptThis makes this first half of September the sixth driest at the Airport based on available records dating back to 1960. Apart from the first half of September of 2012 which yielded just 2.3 mm, no other such first half has been drier since 1990.

The low rainfall figures appear to be due mainly to the pressure across the North Atlantic being higher than normal or a positive North Atlantic Oscillation. This translated into a persistently stable and relatively dry atmosphere, and hence minimal rainfall.

While these figures are interesting, they don’t tell us where the month will end up overall. A few days of wet weather, which we are hoping for, could drastically alter the statistics. So we’ll have to wait for the full-month figures before making any judgements.

While there is no dramatic rainfall expected, several weather models are indicating healthy probabilities for showers over the next several days, particularly Sunday-Monday when the next tropical waves is expected in the area. However, models also are forecasting the NAO to remain positive. Thus, the total for the second half of the month could be similar to that of the first half.

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Antigua’s Rainfall Intensity – 2013

13 03 2014

By Dale C. S. Destin |

Antigua’s water crisis has intensified as the blame for the crisis shifts to low rainfall intensity as opposed to drought. Late last week, the Antigua Public Utility Authority (APUA), the country’s water authority announced that the water level at Potworks Dam – the country’s largest water catchment, was too low for further extraction. February 21 APUA indicated that there was only one month of surface water remaining with the Potworks Dam only having two weeks supply remaining. Meanwhile, the blame for the water crisis seems to have shifted from insufficient rainfall to insufficient intensity of the rainfall for 2013. Last week, it was shown that the rainfall total for last year was near normal. The rainfall measured was 46.20 inches, the equivalent of 72.2 billion gallons of water falling on the island in 2013. RainfallIntensity2013a

The discussion has now shifted to whether the rainfall intensity was below normal. Already, persons in authority have made emphatic pronouncements that the rainfall intensity was in fact below normal. Hence, there was not enough run off to replenish surface catchments.

However, freely available data from the Antigua and Barbuda Met Service do not corroborate that assertion. Rainfall intensity is defined as the rate of rainfall expressed in a number of ways such as millimetres (mm) or inches per hour or per day. So, a simple way of doing this is to divide the total rainfall for a given month or year by the number of days with rainfall greater than or  equal to one mm (SDII method). The intensity can also be determined by counting the number of heavy rainfall days i.e. days with 10 mm or more (threshold method).

Regardless of how you bisect and trisect the Antigua rainfall numbers for intensity, the picture remains the same – normal to above normal intensity occurred in 2013. Hence, asserting the country had below normal rainfall intensity is just not consistent with the reality. For 2013, using the SDII method the intensity was 8.4 mm per day, the same as the normal of 8.4 mm per day. Using the threshold method, 2013 had 33 heavy rainfall days, which is above normal, compare to the normal of 26.3 days for any given year.

Last week’s blog entitled Antigua’s Water Crisis seems to have unintentionally rubbed some persons the wrong way and misunderstood by some others. For clarity, these are the substantive issues that were raised and should be addressed: a) the lack of a comprehensive drought plan administered by stakeholders; the under optimization of catchments and under utilization of groundwater resources; the non-preparation of the population for the water crisis, and whether 72.2 billion gallons of water were enough to prevent or delay the crisis.





Antigua’s Water Crisis

4 03 2014

By Dale C. S. Destin |

Antigua is on the verge of running out of water. According to the Antigua Public Utilities Authority (APUA), the water authority, the island is experiencing a water crisis stemming from the current drought, which dates back to late summer 2013. The water authority has indicated that there was only one month’s supply of surface water remaining as of February 21 and most of the limited water flowing through the country’s taps is from the desalination of seawater.

2013 Rainfall vs NormalThis news came as a thief in the night for most residents. At the beginning of the crisis in January, after days of dry taps and silence, APUA eventually issued a statement blaming a downed water plant and being out of water treatment chemicals which they said would be rectified in days. Then, after more silence and the problem unresolved, they then announced that the country was almost out of water due to the drought. However, the rainfall numbers for 2013 don’t support the dire circumstances being painted by the water authority. Whereas the rainfall for 2013 was not typical, with the dry season wetter than the wet season, the aggregate at the end of the year was near normal.  The actual figure was 46.20 inches for 2013 as compared to the normal of 47.37 inches for a given year.

Digging deeper into the numbers, seven months of 2013 had above normal rainfall, two had near normal rainfall and only three months had below normal rainfall – February, July and October (click image for larger view). Six months had over four inches of rainfall and four months had over five inches, one more than normal in each case. If near normal rainfall is now the threshold for plunging Antigua into a water crisis, then it means that about seven out of every 10 years, this predicament can be anticipated. This could result in major socio-economic problem for Antigua as the success of a country is closely linked to adequate freshwater supplies.

There is no gainsaying that there is a drought. However, it has been slight to moderate for much of the time, apart from a very brief period over July to September when there was a serious rainfall deficit, due almost exclusively to a very dry July.

The logical question then is, “why is Antigua running out of water?” The rainfall for 2013 is more than enough to serve the country’s needs. The 46.20 inches of rainfall is the equivalent of 72.2 billion gallons of water falling on Antigua during 2013. Why has APUA failed to capture enough of this water for storage for the dry season? Why is it that nearly all of it was allowed to runoff into the sea? If Antigua is a “drought prone” country, why haven’t there been strategies and institutions put in place to effectively mitigate and adapt to this hazard? Where is the national drought plan? Better can and should be done.








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