The big story this week in the tropics is wind shear – everywhere.
Wind shear, or the change in wind speed or direction with height, is a major deterrent to tropical formation. It can act like garden shears to a hedge, lopping off the tops of thunderstorms before they’re able to grow and solidify into an organized tropical storm or hurricane.
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The presence of wind shear isn’t always a hurricane-buster. In some cases, hurricanes can strengthen under moderate or even strong shear when the orientation of the hurricane’s outflow is such that it counteracts the harmful upper winds.
As a general rule, however, once vertical wind shear exceeds 20 knots, significant development becomes less likely, above 30 knots, you can usually forget about development in the deep tropics, and above 40 knots it’s very uncommon for storms to strengthen no matter where they’re located.
This week across the tropical formation areas from the Gulf of Mexico through the Caribbean and into the Atlantic, wind shear will be running well above average.
Wind shear typically picks up in October, especially in the Gulf with the passage of regular cold fronts, but this week it’s exceptionally high everywhere. Wind shear exceeds 40 knots through much of the tropical Atlantic and is as high as 60 knots in some areas.
A very active subtropical jet stream will keep the shear persistently strong for the foreseeable future, which means you can rest assured no late-season trouble for now in the tropics.
