Invest 90L in the Tropical Atlantic
Hi everybody, Dr. Rob Carver filling in for Dr. Masters while he's on vacation.
NHC has designated an area of thunderstorms in the tropical Atlantic as Invest 90L (8.5 N, 30.0 W). Microwave remote sensing suggests there are some decent storms in 90L, peak rain rates were around 1-2 inches/hours. According to CIMMS wind-shear analyses 90L is under 10-15 knots of shear with positive divergence aloft. The former isn't quite favorable for further development as it will ventilate the system, but the latter is favorable because it will aid in removing outflow from the storms. There's also a broad area of weak shear to the west and northwest of 90L's current position. Looking at the 500 mb height patterns, the steering currents for 90L are to the WNW, which will move it into the area of weaker shear and get it further away from the equator. This is important because if 90L stays south, it will have trouble developing a circulation. It will have a better chance of becoming a tropical cyclone once it goes north of 10N. The Saharan Air Layer is lurking just to the north of 90L. A WNW track would keep 90L out of the SAL, which is good for development.
Fig. 1 IR Satellite Composite of 90L taken at 540 PM EDT.
Fig. 2 Saharan Air Layer analysis courtesy of CIMMS.
Model Forecasts and Climatology
The 12Z Canadian model moves 90L to the WNW and develops tropical-storm force winds at the surface. The 12Z and 18Z GFS runs are less aggressive in intensifying 90L and adjusts the track so that 90L is moving to the WNW. Based on the run-to-run consistency, previous model verification (i.e. the Canadian model's tendency to overdo intensification), general synoptic pattern, I favor the GFS solution for now. Looking at climatology based on research done by Dr. Bob Hart at Florida State University, none of the tropical cyclones that passed within 1 degree of 90L's current position has ever made landfall. We'll have to keep an eye on this storm, but I don't think it's likely to be a major threat to the Caribbean or US.
Dr. Masters says he'll update this blog entry with a discussion of the Moscow heatwaves later tonight.