Invest 90L is likely to develop into a tropical cyclone by Sunday morning, and will likely make landfall somewhere between the western Florida Panhandle and eastern Louisiana. The National Hurricane Center (NHC) now gives 90L a 70 percent chance of development within 48 hours, and a 90 percent chance within five days. Models have come into better agreement from yesterday, and it appears likely that the Atlantic will see a pre-season named storm for the fourth season in a row. An Air Force Hurricane Hunter reconnaissance aircraft is scheduled to investigate 90L on Friday afternoon, if necessary. Heavy rain remains the primary threat with 90L, although it looks like it may be a little stronger than originally anticipated.

As of 18:00 UTC Thursday, Invest 90L was centered near 19.6°N 88.2°W, and was nearly stationary. Maximum sustained winds were 30 knots (35 mph), with an estimated minimum pressure of 1009 mb. 90L still lacks a well-defined circulation, and the shower and thunderstorm activity is sheared to the east of the broad center. However, environmental conditions are expected to become more conducive for development by Saturday. 90L is likely to form into a subtropical or tropical depression by late Saturday. I personally think it will be more tropical than subtropical, although the heaviest rainfall is still likely to be east of the center. 90L is expected to be over fairly warm waters of about 27-28°C (80.6-82.4°F), with wind shear expected to drop below 20 knots (25 mph). The environment around 90L is also expected to be somewhat moist, which would aid development.

The model guidance has become more aggressive with the development of 90L today. The 12z Thursday GFS, ECMWF and CMC models all predicted 90L to develop into a tropical storm by early Sunday northeast of the Yucatan Peninsula, with a landfall as a moderate to strong tropical storm somewhere between New Orleans and Pensacola early Monday. Although the track is a bit more clear today, it is still a bit uncertain since a well defined center has not yet formed. With a ridge of high pressure expected to build in, 90L (likely to be Tropical Storm Alberto by that time) is likely to take a turn to the northwest on Sunday and steering currents may become weak, slowing down movement. An alternative possibility is the ridge becomes too strong and upwelling causes 90L to dissipate over the Gulf of Mexico without making landfall, but this scenario does not seem likely at this time. The 12z UKMET model is an outlier, taking a weak low inland into the Florida Peninsula. With the models becoming more aggressive on intensity, 90L may be a little stronger than predicted earlier this week. Although wind shear is likely to still be too strong for rapid development, 90L could produce maximum sustained winds of up to 60-70 mph at peak intensity.

Even though winds may be stronger than previously expected with 90L/possible Alberto, heavy rain remains the primary threat. The heaviest rains are still expected to be to the east of the center due to moderate southwesterly shear. Isolated tornadoes may also be possible, especially in the right-front quadrant. Rainfall totals may exceed five inches in some areas across the southeastern United States, with isolated higher amounts possible.

I will be back with another post on 90L sometime tomorrow, possibly in the evening if 90L gets classified as a tropical cyclone or potential tropical cyclone.