Shear rules!

The tropical wave near Puerto Rico that was close to becoming a tropical depression yesterday is looking very disorganized this morning, and I imagine NHC will cancel the reconnaissance mission that was scheduled to fly into it this afternoon. The wave was probably hurt by its interaction with the big islands of Puerto Rico and Hispanolia, but the primary reason for its demise was the large area of high wind shear that pushed down on it from the north. This morning's wind shear analysis from University of Wisconsin's CIMSS shows a large upper level cold-cored low pressure system just north of Puerto Rico, which is bringing wind shear values of up to 50 knots over the northern portion of the tropical wave. Usually, wind shear values above 20 knots are sufficient to keep a tropical depression from forming, so it is no wonder this tropical wave had trouble last night as the big cold low slid to the south and brought such strong shearing winds with it.



The wave is continuing to the west and bringing heavy rains to Hispanolia, but the path in front of it has plenty of strong shearing winds, so development is unlikely. Similarly, the rest of the tropics have some of the highest levels of shear we've seen this hurricane season, so it looks like a quiet next few days. With the demise of Franklin last night, today is the first tropical storm-free day since July 2!

Dr. Jeff Masters