With Tropical Storms Lee and Maria expected to both turn extratropical on Saturday, the 37-day streak with an Atlantic tropical cyclone active at all times is in jeopardy. There are two new tropical disturbances that may develop into a tropical cyclone over the next few days (including Invest 99L) – but neither is likely to become a hurricane or a major threat. The first one, Invest 99L, is a weak area of low pressure located just inland over Southern Florida. The second one is a tropical wave that has a low to chance to develop next week when it is near the Bahamas. However, model support for both disturbances is limited, and neither disturbance is showing significant signs of organization at this time.

Invest 99L still may develop, but on which side of Florida?

A weak area of low pressure has developed over Southern Florida (Invest 99L). This area of low pressure has a low to medium chance of becoming a tropical depression or storm during the next few days. As of 00:00 UTC Saturday, Invest 99L was centered near 27.4°N 80.8°W, and was moving slowly northward. Maximum sustained winds were 25 knots (30 mph), with an estimated minimum pressure of 1011 mb. Although a weak low pressure area is now present, the convective activity is sparse and very poorly organized. I personally think that 99L will have trouble developing organized deep convection due to its proximity to land and the fact that wind shear is expected to increase to the high range, above 30 knots, in just 24 hours. However, if 99L can remain just offshore on either side of Florida, development could occur, although I’m expecting it to be a very weak tropical cyclone if it does develop. Although nearly all of the global models predict that a low pressure area would form, none of the reliable models appear to develop 99L into a tropical cyclone. The National Hurricane Center (NHC) gives 99L a 40 percent chance of development, both within 48 hours and five days. I believe these chances may be too high, and I give 99L only a 20 percent chance of development in 48 hours. If 99L does develop into a tropical storm, it will be named Nate.

Another tropical wave has a low chance to develop

A tropical wave, located over the extreme northeastern Caribbean Sea, is producing some disorganized showers and thunderstorms. The wave currently lacks organization, and conditions are not expected to be favorable for development during the next few days. Conditions could become a little more favorable towards the middle of next week, when the wave is expected to be near the Bahamas. The 00Z Friday ECMWF model run predicted some slight development would occur, but none of the reliable models at 12z developed the wave. The NHC gives this wave a near zero percent chance of development within 48 hours, and a 20 percent chance within five days. Even though development does not appear very likely, it will definitely need to be watched closely.

I will be back with another post tomorrow.