July Headwinds Across the Caribbean

July is a notoriously hostile month for young tropical systems reaching the Caribbean. Here’s why.

Thursday morning satellite showing the Saharan Air Layer stretching across the deep Atlantic and Tropical Storm Don in the north-central Atlantic. Credit: NOAA.

July is a tough month to be a fledgling tropical storm or wannabe hurricane in the Caribbean. Hurricanes have certainly happened in the Caribbean in July. In the 173-year hurricane record, 15 hurricanes have passed through the Caribbean in July – some strong like Category 5 Emily and Category 4 Hurricane Dennis, both in 2005. But one hurricane on average every 12 years isn’t altogether impressive. By August, hurricanes in the Caribbean become much more common – one in about every 3 years.

Of course, hurricanes are generally more common in August across the Atlantic, but that doesn’t altogether explain the difference. Even though the number of tropical formations jumps by 30-40% from June to July basin-wide, the number of formations in the Caribbean is actually sliced in half from June. Not only is the Caribbean a tough place to be in July, it’s especially tough for tropical saplings.

One of the main culprits behind the July struggles of systems here is an acceleration of east-to-west flowing trade winds through the central Caribbean, which peaks in July.

Low-level east-to-west flowing winds accelerate in the central Caribbean – a feature known as the Caribbean Low-Level Jet. The bottleneck of winds peaks in July, creating a less favorable environment for storm formation.

This bottleneck of strong surface winds is known as the Caribbean Low-Level Jet and the increasing winds lead to sinking air across the eastern Caribbean, which works to snuff out building storms. The faster trade winds also can enhance storm-debilitating wind shear across the Caribbean during July.

Needless to say, it’s usually an uphill battle in the Caribbean this time of year when disturbances come along.

We continue to follow the tropical wave in the eastern Atlantic that will be headed toward the Caribbean for early next week.

The disorganized system, currently moving through the eastern Atlantic, hasn’t changed much in organization since yesterday. As we discussed in Wednesday’s newsletter, it has several obstacles ahead, including a good dose of dry air that will pump the breaks on development.

Nevertheless, models do hint at some gradual organization by late weekend and early next week. For now, interests in the Lesser Antilles should follow its progress over the weekend for inclement weather it could bring by late next Monday into Tuesday.

Elsewhere, Tropical Storm Don caught its second wind over the open North Atlantic, strengthening a little late yesterday. Don will slingshot farther out to sea next week and poses no threat to land.

Nearer to Florida and the U.S. the tropics will remain quiet into next week.