|Tropical Depression Three||Winds: 30 kt|
|Pressure: 1013 mbar|
|Advisory 1 / 5:00 PM EDT Mon July 22, 2019|
The area of disturbed weather in the Bahamas has somewhat unexpectedly organized into a tropical depression this afternoon. Visible satellite imagery over the course of the past few days indicated a very sharp wave axis, but it did not depict a well-defined circulation or organized convective activity. That has changed today, with a wide swath of shower and thunderstorm activity that has become more centrally focused since noon. Two ASCAT passes from around that time indicated a closed and organized surface low. One pass actually registered tropical storm-force winds east of Andros Islands, but it is likely these values were influenced by shoaling and not representative of the cyclone's strength. Therefore, without completely discounting the possibility that a tropical storm has formed, the initial intensity is set to 30kt.
The storm system has been interacting with an excessively strong convectively-suppressed kelvin wave over the past few days, and it is embedded within a region of high environmental pressures. These two factors were initially expected to curtail development. What appears to have happened is that the system was able to maintain its vigor until reaching the western Bahamas, where the effects of the kelvin wave have subsided -- and in fact have been replaced by a favorable, convectively-coupled wave -- and abnormally high ocean temperatures around 31C have provided sufficient instability for convective formation. Thus, with wind shear expected to be light for an additional 36 hours, and the storm's track expected to remain east of Florida, the stage appears set for maintenance, if not some slight development in the short term, and it is not out of the question that Three becomes a tropical storm, Chantal, tomorrow. After 36 hours, the environment will become increasingly hostile as a front impinges on the cyclone, and dissipation is expected about 48 hours from now.
Three is being steered on the southwest periphery of a broad mid-level ridge across the central Atlantic. As the storm rounds the edge of this ridge, and moves toward a weakness between the ridge over the Atlantic and one over New Mexico, it should curve northwest then north and finally northeast. There is some model discrepancy regarding the sharpness of this recurve, with models such as the GFS bringing the remnants of the cyclone ashore in North Carolina. This appears to be a western outlier right now, with the most likely solution being that Three remains offshore the East Coast.
FORECAST MAX WINDS
INIT 22/2100Z 30 KT 35 MPH
12H 23/0600Z 30 KT 35 MPH
24H 23/1800Z 30 KT 35 MPH
36H 24/0600Z 30 KT 35 MPH48H 24/1800Z...ABSORBED BY FRONT