Mid-August marks the point where tropical cyclone activity starts to increase significantly in the Atlantic Basin and almost on cue a large and vigorous tropical wave entering the Caribbean Monday has some potential to develop and impact the Cayman Islands later this week.
The westward-moving tropical wave, which was re-designated Invest 93L by the National Hurricane Center in Miami Monday morning after it was dropped over the weekend, was given a low 20 per cent chance of developing into a tropical cyclone through Wednesday.
“There are no signs of a surface circulation and pressures are not falling significantly with this disturbance,” wrote National Hurricane Center forecaster Stacy Stewart. “However, environmental conditions are expected to be marginally favourable for some development of this system during the next few day.”
Cayman Islands National Weather Service Chief Meteorologist John Tibbetts said even if the wave were not to develop, it was still likely to bring about two inches of rain to Grand Cayman when it passes the area on Friday.
Mr. Tibbetts said the hurricane season was moving into what is commonly known as the Cape Verde season, the time when there are increasing numbers of tropical waves coming off the coast of western Africa near the Cape Verde Islands. In addition, he said this was the part of the season where environmental conditions are better for the formation of tropical cyclones.
“The sea temperatures increase,” he said, noting that sea surface temperatures in the Caribbean are already above normal.
In addition, this is the time of the year when cyclone-inhibiting wind shear decreases at the same time and the current neutral El Nino Southern Oscillation was likely to keep the wind shear low for the next couple of months.
With Tropical Storm Gert forming over the weekend, there have already been seven named storms in the Atlantic Basin this year. On average historically, the seventh named storm doesn’t occur until 16 September, a month away.
This year’s season has been active with regard to named storms, but most have been rather weak and short-lived so far and there have been no hurricanes yet. On average, the first hurricane of the season occurs on 10 August.
The National Hurricane Center in Miami issued its updated seasonal forecast on 4 August, increasing its pre-season forecast to 14 to 19 named storms, seven to 10 hurricanes and three to five major hurricanes.
The Atlantic hurricane season runs from 1 June through 30 November.
However, the US Atlantic Oceanographic and Meteorological Laboratory states that 87 per cent of Category 1 and 2 hurricanes and 96 per cent of major hurricanes of Category 3 or above occur in August through September.
The accepted peak day of the hurricane season is 10 September.
Mr. Tibbetts noted that Cayman remains more at risk than other locations late in the hurricane season because many of the late-season tropical cyclones originate in the western Caribbean.