Invest 90L was designated Potential Tropical Cyclone Seven by the National Hurricane Center (NHC) on Sunday evening, and has just recently developed into Tropical Storm Franklin over the Northwestern Caribbean Sea based on last-light visible images indicating that the circulation had become better defined. Franklin is the sixth named storm of the 2017 Atlantic hurricane season so far.

As of 11:00 p.m. EDT Sunday, Tropical Storm Franklin was centered near 16.4°N 83.0°W, and was moving west-northwestward at about 13 mph. Maximum sustained winds were 35 knots (40 mph), with an estimated minimum pressure of 1006 mb. Franklin is expected to strengthen some before landfall, and a Tropical Storm Warning has been issued from the coast of Mexico from Chetumal to Campeche. A Tropical Storm Watch is in effect from Belize City northward to the border of Mexico.  An Air Force Reserve Hurricane Hunter Aircraft is scheduled to visit Franklin tomorrow afternoon. Franklin is expected to strike the central Yucatan Peninsula as a moderate to strong tropical storm with winds near 60 mph.

Weakening is likely while Franklin crosses the Yucatan Peninsula by early Tuesday. However, the cyclone is expected to strengthen somewhat rapidly when it emerges over the Bay of Campeche. Wind shear is expected to be light (less than 15 knots), while sea surface temperatures are expected to be very warm at near 30°C (86°F) with mid-level relative humidity values above 70 percent. The 12z Sunday GFS and ECMWF runs both predicted that Franklin would intensify into at least a category 1 hurricane before landfall south of Tampico, Mexico. Although the official NHC forecast does not quite bring Franklin to hurricane strength, they did mention the possibility. I give Franklin a 60 percent chance of becoming the first hurricane of the season by Thursday over the Bay of Campeche since conditions are expected to be very favorable for intensification. Residents of Mexico should closely monitor the progress of Franklin.

99L becoming less likely to develop

Invest 99L over the tropical Atlantic has become less likely to develop as it has struggled to organize. NHC now only gives it a 10 percent chance of development within 48 hours, and a 30 percent chance of development within five days. Nearly all of the latest global model runs do not show development of 99L. However, it will need to be continued to watched for possible development near the United States East Coast.

I will be back tomorrow with an update on Franklin, and will possibly discuss 99L if it is still a threat to develop.