February 2020 To Be Among The Wettest On Record – Dale Destin


According to meteorologist Dale Destin, this February is on track to becoming one of the wettest on record for Antigua. Thus far, it is the wettest February, at the V. C. Bird International Airport (VCBIA) since 2005 and the wettest for Antigua since 2004.

It has been the wettest first two weeks of February, at the VCBIA, since 2002. The rainfall total of 55 mm (2.17 in), at the end of February 14, at the Airport, is well above normal – in the top 10 percentile on record dating back to 1962. It is more than twice the average – 25.4 mm (1.0 in), for the same period and the fourth wettest on record. Only three other times February 1-14 has been wetter, at VCBIA: 1997 – 66 mm (2.60 in), 1982 – 59.7 mm (2.35 in) and 2002 – 56.8 mm (2.24 in).

Heavy rainfall days (days with 10 mm – 0.40 in, or more) are fairly rare for February, at the Airport. There was none since 2009; however, already for this Feberuary, there have been three recorded. This ties with 2005, 1991, 1982, 1981 and 1976 February for the most number of heavy rainfall days, at VCBIA. The three heavy rainfall days tie with those of February 2005, 1991, 1982, 1981 and 1976. This record will likely be broken by the end of the month.

There is no daily breakdown of the island-average rainfall; however, based on the fact that the current island-average total of 59.9 mm (2.36 in) is already the most since 2004, and the average for the month is 55.9 mm (2.20 in), it is highly likely that the rainfall for the first two weeks of February was also well above normal for the island.

The cause of our wetter than usual February weather is the positive North Atlantic Oscillation (NAO) index. The NAO is a large-scale seesaw in atmospheric pressure between the subtropical (Atlantic) high and the polar low.

The positive NAO index occurs when the subtropical high is higher (stronger) than usual and the polar low is deeper (lower) than usual. When this happens, it causes the winds across the area to be higher than usual (fresh to strong), which in turn destabilises the lower atmosphere by way of mixing and convergence – resulting in above normal rainfall for Antigua and likely other nearby islands.

When the NAO is above normal, the mean rainfall for Antigua for February is 62.7 mm (2.47 in) plus or minus 11.4 mm (0.45 in). These numbers are based on a 95% confidence interval and a probability value (p-value) of 0.009.

A positive NAO index also has implications for other places. For example, the United Kingdom, Ireland and northern Europe get more and stronger winter storms when the NAO index is positive, which have been happening. Thus far, there have been four named winter storms to significantly impact the area, the last being Storm Dennis.

The NAO index is forecast to remain above normal; hence, wetter than usual conditions are expected to continue. Unfortunately, the NAO index is not predictable beyond two weeks; thus, only short-range forecasting can be done using it as a predictor. Also, for some other months, a positive index is associated with below normal rainfall.

The wettest February for the VCBIA and Antigua, on record dating back to 1928, is 1982 with 110.5 mm (4.35 in) and 130.8 mm (5.15 in) respectively. The wettest February 1-14 at the VCBIA is 1997 with 66 mm (2.60 in).

The average rainfall totals for February for the VCBIA and Antigua are 44.9 mm (1.77 in) and 55.9 mm (2.20 in) respectively. This February could be among the top three wettest on record.

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