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| #1148778 (Received by flhurricane at: 4:51 PM 21.Aug.2023) TCDAT3 Tropical Storm Franklin Discussion Number 5 NWS National Hurricane Center Miami FL AL082023 500 PM EDT Mon Aug 21 2023 Franklin is not an especially well-organized tropical cyclone this afternoon. The NOAA reconnaissance mission has been sampling the storm for a large part of the afternoon, and found a center to the south of where the position was estimated earlier today. In addition, the winds on the southwest side of the circulation are more diffuse, and overall the circulation is a bit more elongated than what the plane found yesterday at this time. Peak 850-mb flight level winds were at 48 kt just to the northwest of the circulation, which supports an intensity between 40-45 kt after using a standard reduction. The initial intensity will remain at 45 kt for this advisory, which is also in between the higher TAFB and lower SAB intensity estimates. The tropical storm has been meandering today, and my best guess at an initial motion is a drift south of due west at 265/4 kt. Given the current elongated nature of the surface circulation, the short- term track forecast is tricky, ranging from the GFS on the east side of the guidance envelope that has a center reformation to the northeast, and the CMC and ECMWF which are on the western side of the guidance envelope. The steering currents are also poorly defined currently due to a large mid-oceanic trough in the western Atlantic disrupting the flow pattern. Mid-level ridging eventually builds in to the east of Franklin, which should ultimately induce a northward motion by 24-36 h, and then northeastward between 48-96 h, as a mid-latitude trough reinforces the weakness to the north of the storm. The track guidance has slowed down again compared to the previous cycle, prolonging the time the system will remain over the Caribbean Sea before it moves over Hispaniola. The NHC track forecast is once again slower than the previous cycle and has also been nudged a touch westward compared to the previous one, but is now a bit east of the simple and corrected consensus aids. Given Franklin`s current structure, I am somewhat skeptical there will be a lot of meaningful near-term intensification, especially while moderate vertical wind shear continues to disrupt the convective structure. However, both the GFS- and ECMWF-based SHIPS guidance indicate that the shear will briefly drop under 10 kt in about 24 hours, and when combined with warm 29 C sea-surface temperatures, it still seems prudent to show some intensification before Franklin moves inland over Hispaniola. Significant land interaction over the higher terrain will then lead to weakening, which could be underdone here given the current track over some of the most mountainous terrain. After Franklin emerges into the western Atlantic, another round of southwesterly shear may slow the rate of reintensification, and the latest NHC intensity forecast is a bit more subdued than the previous one, once again electing to follow the HCCA consensus aid. Given the complex intensity factors mentioned above, this is a low confidence forecast. KEY MESSAGES: 1. 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. 2. Franklin is expected to bring tropical storm conditions to portions of the Dominican Republic and Haiti beginning on Tuesday where Tropical Storm Warnings are in effect. FORECAST POSITIONS AND MAX WINDS INIT 21/2100Z 14.3N 70.1W 45 KT 50 MPH 12H 22/0600Z 14.3N 70.9W 45 KT 50 MPH 24H 22/1800Z 15.3N 71.3W 50 KT 60 MPH 36H 23/0600Z 17.2N 71.2W 55 KT 65 MPH 48H 23/1800Z 19.1N 70.8W 40 KT 45 MPH...INLAND 60H 24/0600Z 20.6N 70.3W 45 KT 50 MPH...OVER WATER 72H 24/1800Z 22.2N 68.7W 50 KT 60 MPH 96H 25/1800Z 23.6N 66.0W 60 KT 70 MPH 120H 26/1800Z 25.6N 65.5W 70 KT 80 MPH $$ Forecaster Papin |
