Issued at 500 AM AST Sun Aug 27 2023
000 WTNT43 KNHC 270858 TCDAT3 Hurricane Franklin Discussion Number 27 NWS National Hurricane Center Miami FL AL082023 500 AM AST Sun Aug 27 2023 After becoming obscured for a time earlier tonight, the eye of Franklin is beginning to re-emerge on infrared satellite images early this morning. The last helpful microwave pass at 0246 UTC showed some disruption of Franklin's inner core that could have been due to southerly shear causing the eyewall to be open to the east. This structure was also observed by both NOAA and Air Force Reconnaissance missions earlier tonight. Intensity estimates from SAB and TAFB were both T4.5/77 kt this morning, but with the recent re-emergence of the eye, the advisory intensity is bumped up to 80 kt for this advisory. Franklin is moving to the northwest this morning with an estimated motion of 320/7 kt. The track forecast over the next 48 h is relatively straightforward as the cyclone is expected to round the western side of a mid-level subtropical ridge to its east. The track guidance over this time span is in good agreement, and the latest NHC track forecast is very close to or just a bit west of the prior one through 48 h. Afterwards, uncertainty quickly increases, primarily related to whether Franklin will be captured by a mid-latitude trough emerging off the eastern US coastline. While the GFS continues to show the hurricane being captured by this trough, the latest runs of the ECMWF, CMC, and UKMET now leave the cyclone behind, resulting in it turning more eastward and slowing down as the trough bypasses it to its north. Both the ECMWF and GFS ensembles show a huge amount of spread, spanning more than 1000 mi at the end of the forecast period. While the latest NHC track forecast will not shift all the way to Franklin being left behind by the trough, it is noticeably slower and eastward compared to the prior track at days 4 and 5. Future adjustments to the southeast may become necessary in subsequent cycles. On the forecast track, Franklin will be making its closest approach to Bermuda in 3-4 days, and is a bit closer to Bermuda than the prior advisory. As long as the small eyewall observed by earlier recon and microwave imagery is closing back off, Franklin should continue to intensify, likely rapidly due to favorable low shear and ample warm waters under the hurricane. DTOPS continues to suggest between a 59-68 percent chance of a 30 kt intensity increase in the next 24 hours, and the latest intensity forecast is close to this scenario, taking the storm to a category 3 hurricane in 24 hours and peaking it as a 115-kt category 4 hurricane in 36 hours. This is near the higher end of the intensity guidance, but is quite close to the latest HFIP corrected consensus forecast. Afterwards, there are a couple of factors that could cause Franklin to start weakening. First, the storm will likely undergo fluctuations related to eyewall replacement cycles, which would also broaden its overall wind field. In addition, the motion of Franklin is relatively slow, and the warm 29-30 C waters it will be traversing are fairly shallow, leaving the cyclone prone to cool upwelling along its track as the wind field expands. Vertical wind shear out of the northwest also increases after 36 hours. All of these factors are why the latest NHC intensity forecast shows weakening beginning after this period, which is also in good agreement with both the simple and corrected consensus aids. Given the large spread of solutions at days 4 and 5, it is unclear if Franklin will start to undergo extratropical transition during that time, or will be left behind by the trough, resulting in a slower motion that stays over warmer waters south of the Gulf Stream. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 24.7N 68.7W 80 KT 90 MPH 12H 27/1800Z 25.6N 69.4W 90 KT 105 MPH 24H 28/0600Z 26.9N 70.3W 105 KT 120 MPH 36H 28/1800Z 28.4N 70.6W 115 KT 130 MPH 48H 29/0600Z 29.9N 70.4W 110 KT 125 MPH 60H 29/1800Z 31.3N 69.5W 100 KT 115 MPH 72H 30/0600Z 33.0N 67.9W 90 KT 105 MPH 96H 31/0600Z 36.5N 61.0W 80 KT 90 MPH 120H 01/0600Z 40.0N 52.0W 70 KT 80 MPH $$ Forecaster Papin
