Issued at 200 PM CVT Mon Aug 11 2025
000 WTNT45 KNHC 111447 TCDAT5 Tropical Storm Erin Discussion Number 1 NWS National Hurricane Center Miami FL AL052025 200 PM CVT Mon Aug 11 2025 The system we have been monitoring that moved across the Cabo Verde Islands over the past 6-12 h (Invest 97L) has maintained a small, but persistent area of deep convection. This activity prompted an earlier TAFB subjective Dvorak fix of T2.5/35 kt suggesting the convection is now sufficently organized to be classified as a tropical cyclone. We also received scatterometer data at 1107 UTC with a peak wind retrieval of 39 kt embedded in this convection, with an ambiguity analysis suggesting the circulation is also well defined, albeit still somewhat elongated on the eastern edge. The combination of all this data suggests that a tropical storm has formed, and NHC is initiating advisories on Tropical Storm Erin with a current intensity of 40 kt. Erin is moving quickly off to the west, with the motion estimated at 275/17 kt. Over the next few days, this motion should continue with possibly some slight south-of-due-west motion. Erin's motion is primarily influenced by an east-to-west oriented mid-level ridge draped across the subtropical Atlantic basin. By the end of the forecast period, this ridge may start to become more oriented to the northeast of Erin, inducing a more poleward motion by 120 h. The initial NHC track forecast elects to stick fairly close to the HFIP corrected consensus approach (HCCA), which is a touch on the south side of the overall track guidance envelope. It should be noted that spread in the track guidance, especially the ensembles, begins to increase markedly at the end of the forecast period. The intensity forecast in the short-term is a little tricky. The earlier scatterometer data indicate the system has a small circulation which could be prone to rapid intensity changes, either up or down. While vertical wind shear over the system is forecast to be low, between 5-10 kt over the next 72 hours, sea-surface temperatures are more marginal, around 26-27C, with a decent amount of dry mid-level air along the path of the tropical storm. The first NHC intensity forecast will thus only forecast slow intensification in the short-term, assuming the marginal SSTs and lack of mid-level moisture will keep the small vortex in check. After 48 h, however, the SSTs start to gradually increase and should allow the local environment of Erin to moisten up. Thus, the rate of intensification will likely increase in the second half of the forecast period. The NHC intensity forecast is a little on the high side of the guidance in the short-term, partially due to the initial intensity, but is in line with the HCCA intensity aid. By 120 h, the hurricane-regional models (e.g., HWRF/HAFS), and statistical-dynamical aids (EC-SHIPS/LGEM) show Erin becoming a major hurricane, and that will be explicitly forecast at the end of the period. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 17.4N 28.0W 40 KT 45 MPH 12H 12/0000Z 17.5N 31.2W 45 KT 50 MPH 24H 12/1200Z 17.4N 35.1W 50 KT 60 MPH 36H 13/0000Z 17.1N 38.7W 55 KT 65 MPH 48H 13/1200Z 17.1N 41.7W 60 KT 70 MPH 60H 14/0000Z 17.4N 45.0W 70 KT 80 MPH 72H 14/1200Z 18.0N 48.4W 80 KT 90 MPH 96H 15/1200Z 19.6N 54.0W 90 KT 105 MPH 120H 16/1200Z 21.5N 60.0W 100 KT 115 MPH $$ Forecaster Papin