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| #1140061 (Received by flhurricane at: 10:44 PM 19.Jun.2023) TCDAT3 Tropical Storm Bret Discussion Number 3 NWS National Hurricane Center Miami FL AL032023 1100 PM AST Mon Jun 19 2023 This evening, Bret`s structure on satellite has evolved from a curved banding pattern to a growing central dense overcast near the estimated center. The exact location of the center is tricky to pinpoint though, most likely positioned just west of the deepest central convection. Dvorak estimates from TAFB and SAB were both T2.5/35-kt at 00 UTC, 37-kt from UW-CIMSS, and unfortunately there have not been any helpful microwave or scatterometer passes this evening. The initial intensity is being held at 35 kt for this advisory in agreement with the majority of the available data. The initial motion appears to be just north of due west at 275/16 kt. A deep-layer ridge that is currently positioned overhead of Bret will initially follow along with the cyclone, maintaining a west or north of due west heading for the next 48-72 hours. As the system approaches the Lesser Antilles later this week, a mid- to upper-level trough is forecast to amplify somewhat, with the vertical depth of Bret likely to influence its future track. Once again there is a large spread in both along and cross track model predictions, with the ECMWF on the south and west end, and the GFS and some of the strongest hurricane regional models (HWRF, HAFS-A) on the north and east end. The consensus aids have shifted ever so slightly south and west from the previous forecast cycle, and the NHC track will follow suit, especially beyond 60-h. However, there continues to be larger than normal uncertainty in the track forecast given the large spread of the guidance suite. In the short-term, environmental conditions remain quite favorable for additional intensification, with shear remaining under 10-kt, and ample mid-level moisture and anomalously warm SSTs maintaining a favorable thermodynamic environment. Thus, steady intensification seems likely for the next day or so. However, between 36-60 h, mid-level moisture begins to markedly decrease along Bret`s forecast track, and both the GFS and ECMWF suggest mid-level northwesterly shear may begin to undercut the more favorable upper-level easterlies. This is where the intensity forecast becomes tricky, since a more vertically coherent system could be more resilient against these less favorable conditions versus one that remains less aligned and more susceptible to dry air intrusion. The intensity guidance also diverges over this time frame, with some of the regional hurricane guidance showing continued intensification, compared to leveling off from the global model guidance. The latest NHC forecast is a bit more conservative at this time frame, but still shows a peak intensity at hurricane intensity between 48-60 h. Thereafter, even drier air and additional shear is likely to begin a weakening trend, and the latest NHC intensity forecast shows a bit more weakening than the previous cycle. KEY MESSAGES: 1. Bret is forecast to initially strengthen and then move across the Lesser Antilles near hurricane intensity on Thursday and Friday, bringing a risk of flooding from heavy rainfall, strong winds, and dangerous storm surge and waves. 2. Given the larger than usual uncertainty in the track forecast, it is too early to specify the location and magnitude of where these hazards could occur. However, everyone in the Lesser Antilles, Puerto Rico, and the Virgin Islands should closely monitor updates to the forecast for Bret and have their hurricane plan in place. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 11.4N 43.5W 35 KT 40 MPH 12H 20/1200Z 11.8N 45.8W 45 KT 50 MPH 24H 21/0000Z 12.3N 48.7W 55 KT 65 MPH 36H 21/1200Z 12.8N 51.4W 60 KT 70 MPH 48H 22/0000Z 13.3N 53.9W 65 KT 75 MPH 60H 22/1200Z 13.8N 56.7W 65 KT 75 MPH 72H 23/0000Z 14.3N 59.4W 60 KT 70 MPH 96H 24/0000Z 15.0N 64.5W 55 KT 65 MPH 120H 25/0000Z 16.5N 69.5W 50 KT 60 MPH $$ Forecaster Papin |
