A new storm is born in the tropics

Good afternoon.

While the weather in the Northeast is generally quiet (although with the typical afternoon thunderstorms that accompany hot and humid air masses), the tropics are starting to come to life. This morning, Tropical Depression Four developed in the eastern Atlantic, well to the east of the Windward Islands. It is forecast to intensify into Tropical Storm Danny soon if it hasn’t already, and possibly to Hurricane Danny later this week.

Track Forecast – Low Rider?

Fact is, this storm is more than 5,000 miles away from the Northeast, and even if it tried to turn towards us, it would be more than 10 days away at least. However, the current pattern seems to suggest it will have trouble gaining latitude. The NHC agrees in its 5 day forecast, keeping it below 15°N latitude on a westward trajectory. That makes it a potential threat for the Lesser Antilles, most notably the Windward Islands, by the weekend or early next week. Some models do track the storm farther north, keeping it north of the islands, but I have a hard time seeing such given the upper-level patterns. Given the well established pattern, I would place the track confidence at Moderate-High.

Current upper level pattern. Notice the ridge building to the north, with a weakness over the Cape Verde to the east. That suggests a track due west.

gfs_z500a_atl_29

Upper level pattern a week from now. Notice the ridge only strengthens.

Intensity Forecast – Shear gone, some dry air

The intensity forecast is more complicated. Outflow is well established around the storm and shear is low in the region, which is a dramatic change from earlier in the month when shear was extremely high. A Kelvin wave nearby has insulated the system from the typical El Nino pattern of high wind shear. There is some dry air but if it can mix it out, then steady intensification is likely. Most models bring the system up to hurricane intensity in the next 3 to 4 days, with the SHIPS pushing it all the way to major hurricane intensity with winds near 120 mph (Category 3). The NHC forecast by Day 5 has the storm as a hurricane with 100 mph winds (Category 2).

However, the small size may result in a storm that is more sensitive to intensity changes, with rapid intensification possible at times and rapid weakening also possible. Shear increases in the eastern Caribbean Sea, so weakening is shown by most models by the time the storm reaches that region. I personally believe that the system will become Tropical Storm Danny soon (if not already), strengthen steadily and become Hurricane Danny by tomorrow or Thursday. If an eye can be established, rapid intensification is possible late Thursday or Friday, perhaps into a major hurricane. However, conditions do become less favorable west of 55°W. Confidence in my intensity forecast is Low-Moderate.

As for the Northeast? This shouldn’t be of any significant concern, and certainly not in the short to medium term. However, the fact that we are coming into late August means we should always keep an eye out on the tropics, as several of the most devastating Northeast storms have hit in this time periods, including Carol, Bob and Irene. We will keep you posted in the coming days.

Forecaster Craig Ceecee (@EternalWeather1)

Leave a Reply