Hold on to Your Hats and Skirts!

31 12 2014

Dale C. S. Destin |

Forecast Wind Speeds - Sun Jan 4, 2015

Forecast Wind Speed – Sun Jan 4, 2015

Hold on to your hats and skirts and batten down the hatches. Strong winds and very rough seas to kick off the new year across Antigua and much of the Caribbean.

The winds will become stronger with peak sustained speed near 25 mph (22 knots) over the weekend across Antigua and Barbuda. The winds will also be very gusty with gusts as high as 37 mph (32 knots) possible, just 2 mph short of storm force.

Forecast Wind Gust - Sun Jan 4, 2015

Forecast Wind Gust – Sun Jan 4, 2015

The strong winds will stirrup very rough seas in our area. Seas could peak as high as 3.6 metres (12 ft) Sunday and continue above 2.4 metres (8 ft) until, at least, the middle of next week. By next Thursday there could be a transition from wind waves to swell waves from a frontal low pressure system.

Forecast Wave Height - Sun Jan 4, 2015

Forecast Wave Height – Sun Jan 4, 2015

The strong winds are in response to the steepening of the pressure gradient across the area. You may recall that winds are the horizontal movement of air. They only occur due to the spatial deferential in atmospheric pressure. The change in pressure across a particular area is called the pressure gradient. The steeper the gradient or greater the pressure difference between two points, the stronger the winds and vice versa.

Warnings are already in effect for hazardous seas that are bound to get much worse. Mariners should consider staying near shore until winds and seas subside, perhaps late next week.

The strong winds could make certain activities uncomfortable, if not dangerous. For example, working at elevation could be dangerous and should be curtailed until the winds return to normal speeds.

The worst conditions will be seen in the western Caribbean Seas, juts north of Columbia. The winds are expected to peak near 44 mph (38 knots) with gusts near 54 mph (47 knots); this is tropical storm strength and under tropical cyclone criteria would require a tropical storm warning. Wave heights will approach 6 metres (20 ft).

This area of storm force winds is pushing large waves outward which will cause most of the Caribbean Sea to be rough for the next several days. Mariners should avoid travelling not only the Atlantic waters of the Caribbean but also the Caribbean Sea, especially the western Caribbean Sea south of Jamaica.

Feel free to share with us your experiences of this strong wind and very rough seas event and follow us on wordpress: anumetservice.wordpress.com twitter: @anumetservice facebook: /anumetservice tumblr: anumetservice.tumblr.com to keep current with weather and climate info.

Happy New Year!

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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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Flying Start to December’s Rainfall for Antigua

7 12 2014

Dale C. S. Destin |

There has been a flying start to the rainfall total for Antigua for December. So far for the month, December 1-5, the rainfall total at the V. C. Bird International Airport is 50.4 mm (1.98”). This is well above normal, the fifth highest on record dating back to 1967 and the second highest since 1981. Relative to this period, only December 1-5, 2012 has been wetter with 57.0 mm (2.24”), in the past 34 years. On average at the Airport, December 1-5, gets 12.6 mm.

A large portion of the rainfall, so far for the month, was due to a deep layer trough system connected to a low pressure area, which formed hundreds of miles north of Antigua. The trough and low are still around; however, not much more rainfall is anticipated as moisture levels are near minimum.

In 48 years, only four other December 1-5 were wetter: 2012, 1981, 1970 and 1968. The record wettest December 1-5 occurred in 1970, when a staggering 114.0 mm of rain fell.

Dec1-5_Rain_GraphicThis very wet start to December has thankfully further quenched the drought, which started in September 2013; however, it is no yet over. The last assessment of the drought indicates that it has eased to slight levels. At least a further 60 mm would bring it to an end.

Will we get the needed amount of rainfall to end the drought? It is not very clear as the climate continues to send mixed signals. The spike in rainfall over the past couple of months seems to be partially due to warmer than normal North Atlantic sea surface temperatures. However, an El Nino appears to be brewing, and if established, could suppress rainfall. Notwithstanding, the forecasts for December and the period December to February (“winter”) are for above normal to normal rainfall. Thus, it is likely that the drought will end or not get any worse.

Of course, while the 50.4 mm so far for December is impressive and invaluable, it does not tell us where the month will end up overall, and there is a slight chance of the upcoming months having below normal rainfall. On average at the Airport, the rest of December gets 71.2 mm (2.80”) of rainfall. In the past this period has had as little as 14.5 mm (0.57’’) and as much as 207.3 mm (8.16”).

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