|
Show Selection: |
| #1107320 (Received by flhurricane at: 11:03 AM 15.Sep.2022) TCDAT2 Tropical Storm Fiona Discussion Number 5 NWS National Hurricane Center Miami FL AL072022 1100 AM AST Thu Sep 15 2022 Moderate westerly shear continues to displace Fiona`s deep convection about a degree to the east of the low-level center, with convective cloud tops as cold as about -80 degrees Celsius. A recent ASCAT pass showed a solid area of 40- to 45-kt winds, and with the scatterometer`s known undersampling characteristics, it`s not out of the question that Fiona`s intensity could be a little higher. For now, the initial intensity will be held at 45 kt, pending additional data from an Air Force Reserve Hurricane Hunter aircraft that is scheduled to investigate the storm this afternoon. Moderate shear, generally out of the west, is expected to continue for much of the forecast period. That in itself should suppress significant strengthening, but it may not be enough to prevent any strengthening at all. Fiona`s current intensity is a testament to its resilience in the face of the shear it has experienced over the past 24 hours. There has been a general uptick in the intensity guidance after 48 hours, and the new NHC intensity forecast has been nudged upward during that time. It is important to note, however, that the official forecast still lies below the IVCN, HCCA, and FSSE consensus aids from day 3 onward, and additional adjustments to the intensity forecast could be required in subsequent advisories if these trends continue. Strong low- to mid-level ridging over the western Atlantic is steering Fiona due west, or 270 degrees at 12 kt, and this general motion, with some gradual decrease in forward speed, is likely to continue for the next couple of days. There is notable model divergence after 36 hours, with the stronger GFS, HWRF, and HMON solutions turning a slower Fiona northwestward over the northern Leeward and Virgin Islands. On the other hand, the ECWMF, UKMET, and all of the consensus aids maintain a faster westward to west-northwestward motion across the far northeastern Caribbean Sea through day 3. Given the expectation that moderate shear is likely to continue, the NHC track forecast favors the less-intense scenarios and shows a solution moving just south of the Virgin Islands and then near Puerto Rico in a few days. After day 3, a weakness near the western extent of the ridge should allow Fiona to gain some latitude and possibly turn toward the northwest, moving across the Greater Antilles into the far southwestern Atlantic. On the whole, the NHC track forecast remains steady from previous predictions, largely following a blend of the TVCN and HCCA consensus aids. Additional watches or warnings will likely be required later today for portions of the Leeward Islands, Puerto Rico, and the Virgin Islands, and interests in these locations should monitor the latest forecast updates. Key Messages: 1. Tropical storm conditions are expected in portions of the Leeward Islands within the warning area by Friday evening. Tropical storm conditions are possible in portions of the Leeward Islands within the watch area by Friday night. 2. Heavy rains from Fiona will reach the northern Leeward Islands Friday afternoon, spreading to the British and U.S. Virgin Islands and Puerto Rico Saturday into Sunday morning, and reaching eastern Hispaniola Sunday. This rainfall may produce flash and urban flooding, along with isolated mudslides in areas of higher terrain. 3. Fiona is expected to move near the Virgin Islands, Puerto Rico, and Hispaniola this weekend and early next week, and watches will likely be issued for some of those areas later today. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 16.6N 54.3W 45 KT 50 MPH 12H 16/0000Z 16.6N 56.2W 45 KT 50 MPH 24H 16/1200Z 16.7N 58.7W 45 KT 50 MPH 36H 17/0000Z 16.9N 61.2W 50 KT 60 MPH 48H 17/1200Z 17.2N 63.4W 50 KT 60 MPH 60H 18/0000Z 17.5N 65.2W 50 KT 60 MPH 72H 18/1200Z 17.8N 66.6W 55 KT 65 MPH 96H 19/1200Z 19.3N 68.6W 55 KT 65 MPH 120H 20/1200Z 21.5N 70.4W 60 KT 70 MPH $$ Forecaster Berg |
