Potential Tropical Cyclone 9 intensifies to become Tropical Storm Isaias1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed Potential Tropical Cyclone Nine as it moved northwestward across the Caribbean Sea on 29 July 2020. In Puerto Rico, Luis Muñoz Marin Airport in San Juan (TJSJ) had a wind gust to 44 knots (51 mph) around 19 UTC. Numerous pulsing overshooting tops were seen, with some exhibiting cloud-top infrared brightness temperatures as cold as -89ºC — according to plots of rawinsonde data from San Juan, Puerto Rico (below), such temperatures were about 10ºC colder than that of the tropopause. Note the significant increase in moisture from the 12 UTC to the 00 UTC soundings, as PTC9 moved closer to Puerto Rico. GOES-16 Infrared images with an overlay of GLM Flash Extent Density (below) revealed a modest amount of lightning activity associated with some of the larger clusters of convection.
===== 30 July Update =====PTC9 continued to organize and intensify, becoming classified as Tropical Storm Isaias at 0300 UTC on 30 July — GOES-16 Infrared images with an overlay of GLM Flash Extent Density (above) displayed persistent overshooting tops (with brightness temperatures in the -85 to -90ºC range) along with intermittent lightning activity. Several large clusters of thunderstorms produced flash flooding across pars of Puerto Rico.
GOES-16 Visible images (below) showed Isaias just after sunrise.