One of the Worst First-Quarter Rainfall Deficits for Antigua

20 04 2015

Dale C. S. Destin |

Antigua is having its seventh driest start to a year on record. As of the end of March, the average first-quarter (January-March) rainfall total for the island was 90.4 mm (3.56 in). Normally, by now, we would have received 176.0 mm (6.93 in). Thus, there is a relatively huge rainfall deficit of 85.6 mm (3.37 in).

MonthlyRainfallAccumulationforAntigua

This is the second consecutive year that first-quarter rainfall is much lower than normal. However, this year’s first-quarter rainfall is 20% lower than last year’s.

The rainfall for January-March is 49% lower than normal. In other words, we have only received 51% or just a little over half of what we normally get for this period.

Top10DriestFirst-QuartersForAntigua

Only six other first-quarter rainfall totals have been lower; however, none since 2001, and only one since 1983.

All three months of the first-quarter have been quite dry. The wettest of the three months, February, was drier than normal and the other two months were the driest since 2002.

This kind of dryness to the start of the year can only be expected to occur once in every 15 years, on average. In other words, the chance of the first three months of a year having such low rainfall is less than 7%.

At the Airport, the number of wet days (with 1 or more mm) up to the end of March was 15. Usually we would have 27 for the first-quarter.

The sluggish start to rainfall for the year seems due mainly to a positive North Atlantic Oscillation (NAO) or higher than normal surface pressure across the Atlantic Ocean. A positive NOA has a cooling effect on sea surface temperatures (SSTs), which in turn causes unconducive atmospheric conditions for rainfall.

Outlooks for the next six months are not very encouraging. Based on SSTs across the tropical Atlantic and Pacific Oceans, the main drivers of our climate, lower than normal rainfall is likely through the next six months.

We are in the dry season and it does not normally rain a lot; however, relative to this time of the year, this first-quarter deficit is enormous, especially against the backdrop of the current protracted drought and a dismal rainfall outlook for much of the rest of the year.

The last time we had a drier start to the year back in 2001, we were in the midst of a severe drought. The eventually rainfall total for that year was 850.9 mm (33.50 in), much lower than normal and drier than last year.

A dry first-quarter does not always signal a dry year (below normal rainfall year). However, of years with the top 10 driest first-quarters, 6 are dry, 2 are normal, 1 is wet and 2015 is to be decided. We will keep you posted.

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