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Only a Few Minor Threat Areas in the Tropical Atlantic

By: Jeff Masters 2:43 PM GMT on September 12, 2015

A tropical wave that moved off the coast of Africa on Thursday was a few hundred miles south of the Cape Verde islands on Saturday morning, and was moving west to west-northwestwards across the Atlantic at about 15 mph. Though the wave does not yet have much spin or heavy thunderstorm activity, conditions are favorable for development, with wind shear a moderate 10 - 20 knots, ocean temperatures at 28°C (83°F), and only a modest amount of dry air from the Saharan Air Layer to the north of the disturbance. One of our three models for predicting tropical cyclone genesis, the UKMET model, forecasted in its 00Z Saturday run that the wave would develop into a tropical depression midway between the Lesser Antilles Islands and Africa by Monday. Many of the 20 members of the GFS ensemble and 50 members of the European ensemble forecast predicted development by Wednesday, though the operational high-resolution versions of these models were lukewarm in their support of development. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 10% and 50%, respectively. It appears likely that this wave will curve to the north well before it can affect the Lesser Antilles Islands. The next name on the 2015 Atlantic list is "Ida".

Figure 1. MODIS image of the tropical wave south of the Cape Verde islands from NASA's Aqua satellite taken at approximately 8 am EDT Saturday, September 12, 2015. The Cape Verde islands are visible at the upper right. Image credit: NASA.

Gulf of Mexico disturbance bringing heavy rains to Mexico
An area of disturbed weather has formed in the Western Gulf of Mexico's Bay of Campeche in association with a cold front that pushed south of Texas and has stalled over Mexico and its offshore waters. This disturbance is bringing heavy rains to the coast of Mexico, but none of our reliable models for forecasting tropical cyclone development are predicting that a tropical depression will form in the Gulf over the next five days, due to high wind shear of 20 - 30 knots. The Mexican Weather Service is warning that rainfall amounts of up to 4" may affect portions of Mexico from this disturbance.

Elsewhere in the Atlantic
NHC is mentioning two other areas of interest in their Tropical Weather Outlook, neither of which are a threat to become tropical cyclones that will fact land. The remains of Tropical Storm Grace are bringing a few showers to Puerto Rico and surrounding islands, but high wind shear will discourage any development. An area of disturbed weather in the Central Atlantic about about 1000 miles southwest of the Azores, far from any land areas, is being given 2-day and 5-day odds of development of 10% and 20%, respectively.

Wunderblogger Steve Gregory has an update on the tropics and on the U.S. "Very Active Early Fall Pattern" setting up in his Friday afternoon post.

Have a great weekend!

Jeff Masters


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