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| #1148607 (Received by flhurricane at: 5:09 PM 20.Aug.2023) TCDAT3 Tropical Storm Franklin Discussion Number 1 NWS National Hurricane Center Miami FL AL082023 500 PM AST Sun Aug 20 2023 This afternoon we have received a wealth of data from both a NOAA reconnaissance mission and satellite imagery near the area of low pressure located in the eastern Caribbean Sea. Earlier visible satellite imagery showed the system had likely formed a tight low-level vortex based on the earlier cloud motions before a convective burst obscured the center. Scatterometer data that clipped the system on the east side also showed winds near tropical storm intensity. The NOAA aircraft flew through the system shortly thereafter, and found the system had indeed formed a well-defined center, with 950-mb flight level winds of 51 kt just to the northeast of the center. All this information confirms that Tropical Storm Franklin has formed this afternoon, with an initial intensity set at 40 kt. The initial motion is off to the west-northwest at 290/12 kt. Over the next 24 hours this general motion should continue while the system remains steered by a narrow mid-level ridge. Thereafter, a large mid-ocean trough over the western Atlantic will produce a pronounced weakness in this ridging, likely causing the tropical storm to make a sharp turn northward, bringing the storm near or over the large island of Hispaniola in about 48-60 h. Afterwards, another mid-latitude trough is forecast to amplify southward, maintaining this weakness, and resulting in Franklin turning northeastward towards the end of the forecast period. There is a decent amount of spread in the track guidance, related to just when Franklin will make the initial northward turn. For this initial forecast, the NHC track forecast will stick close to the track consensus TVCN, which favors a track in between the latest ECMWF and GFS solutions, favoring the GFS a bit more. Intensity wise, Franklin may have to deal with a bit of westerly wind shear in the short-term, limiting more robust intensification early on. However, this shear drops off as the system makes its turn northward towards Hispaniola a bit more intensification is shown with a 55-kt intensity peak as Franklin approaches the coast. The intensity forecast then is complicated by the fact that Franklin will likely pass near or over the island sometime in the 2-3 day time period, and some weakening is shown during this time. However, the forecast environment after the system re-emerges into the Western Atlantic looks mostly favorable, with reintensification likely as long as the system is not too disrupted by the higher terrain of Hispaniola. The NHC intensity forecast is in good agreement with the consensus aids, and lies closest to the HFIP corrected consensus approach through the forecast period. Based on the current track forecast, a tropical storm watch has been issued for the entire southern coastline of Haiti and the Dominican Republic. KEY MESSAGES: 1. Franklin is forecast to approach Hispaniola late on Tuesday and move across the island on Wednesday as a tropical storm, bringing a risk of flooding from heavy rainfall, strong winds, and dangerous waves along the coast. 2. Heavy rainfall from Franklin is expected across portions of Puerto Rico and Hispaniola through the middle of the week. The heavy rainfall may produce areas of flash and urban flooding as well as river rises and mudslides. Across Hispaniola, significant and potentially life-threatening flash flooding is possible Tuesday into Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 20/2100Z 14.6N 67.1W 40 KT 45 MPH 12H 21/0600Z 15.0N 68.9W 45 KT 50 MPH 24H 21/1800Z 15.4N 70.7W 45 KT 50 MPH 36H 22/0600Z 15.8N 71.5W 50 KT 60 MPH 48H 22/1800Z 17.2N 71.5W 55 KT 65 MPH 60H 23/0600Z 19.1N 71.1W 50 KT 60 MPH...INLAND 72H 23/1800Z 21.0N 70.6W 55 KT 65 MPH...OVER WATER 96H 24/1800Z 23.9N 67.5W 65 KT 75 MPH 120H 25/1800Z 25.4N 65.0W 75 KT 85 MPH $$ Forecaster Papin |
