Tropical Storm Franklin has strengthened today as it has approached the Yucatan Peninsula, although the cyclone has not rapidly intensified as much as previously expected. Although additional intensification seems unlikely before its first landfall over the Yucatan Peninsula, Franklin is expected. Aside from Franklin, it is still too soon to write off the struggling Invest 99L over the tropical Atlantic, which has a chance to develop into a tropical cyclone east of the Bahamas.

Franklin likely to weaken over the Yucatán, but could restrengthen into a hurricane over the Bay of Campeche

As of 10:00 p.m. CDT (11:00 p.m. EDT), Tropical Storm Franklin was centered near 19.1°N 87.3°W, and was moving west-northwestward at about 14 mph. Maximum sustained winds were estimated at 50 knots (60 mph), with an estimated minimum pressure of 995 mb based on the earlier data from the reconnaissance aircraft. Despite little change in organization since the last flight, it is possible that this intensity may be a little conservative since Franklin was beginning to strengthen more quickly when the aircraft left the cyclone earlier this evening. Franklin has an unusual structure for a tropical cyclone, with little deep convection near the center. Microwave imagery also showed that the inner core of Franklin was not very well defined. Although a Hurricane Watch was previously in effect for parts of the Yucatán Peninsula, this watch has since been discontinued since Franklin has not strengthened as quickly as anticipated. A Tropical Storm Warning is still in effect for Belize City northward to the Belize/Mexico border, as well as the coast of Mexico from Chetumal to Sabancuy. It is likely that subsidence or dry air entrainment limited rapid intensification of Franklin before landfall. Franklin is expected to make landfall at some point during the next few hours in the Mexican State of Quintana Roo.

Franklin is likely to weaken some tomorrow as it crosses the Yucatán Peninsula, likely to a low-end tropical storm. Franklin is expected to survive the crossing, since the Peninsula is fairly flat. However, Franklin is expected to emerge into the Bay of Campeche by late tomorrow evening. In the Bay of Campeche, environmental conditions are expected to be somewhat conducive for strengthening, with sea surface temperatures of about 30°C (86°F) and mid-level relative humidity values above 70 percent, but moderate northerly wind shear of about 15-20 knots is likely to limit any extreme rapid intensification before landfall. Nonetheless, the official National Hurricane Center (NHC) forecast brings Franklin to hurricane strength over the Bay of Campeche. Franklin is expected to reach hurricane intensity on August 9 – one day before the average formation date of the first Atlantic hurricane, August 10. Franklin is expected to take a southwestward dive towards Veracruz, and a Hurricane Watch has been issued for Puerto de Veracruz to Rio Panuco. Landfall is currently expected during the early morning hours on Thursday. Residents of Eastern Mainland Mexico should closely monitor the development of Franklin.

United States East Coast should keep a close eye on Invest 99L

Invest 99L remains poorly organized with disorganized thunderstorm activity over the central tropical Atlantic, and is unlikely to become a tropical cyclone in the short term due to unfavorable conditions. However, conditions could become a little more favorable for development by the time 99L is in the Western Atlantic Ocean. NHC gives 99L a near zero percent chance of development during the next 48 hours, and a 20 percent chance within the next five days.  The 12z Monday ECMWF and CMC model runs, as well as over half of the 12z Monday EPS ensemble members, predicted that 99L would develop into a tropical depression by the weekend east of the Bahamas. The 12z Monday GFS and UKMET model runs did not predict that 99L would develop into a tropical cyclone.

The 12z Monday operational ECMWF run developed 99L into a tropical storm by Saturday east of the Bahamas, and strengthened it into a moderate to strong tropical storm off the North Carolina coast. Many EPS ensemble members also showed this scenario; in fact, a few of the members developed 99L into a hurricane very near the United States East Coast. It is too soon to predict the exact track or intensity if development occurs, but residents along the United States East Coast should monitor the progress of 99L over the coming days. The next name on the Atlantic naming list is Gert.

I will be back tomorrow with another post on Franklin and 99L.