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Tropical Storm Michael Forecast Discussion Number 6
2018-10-08 04:57:13| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT Sun Oct 07 2018 000 WTNT44 KNHC 080257 TCDAT4 Tropical Storm Michael Discussion Number 6 NWS National Hurricane Center Miami FL AL142018 1000 PM CDT Sun Oct 07 2018 On the last outbound leg to the north, the Air Force Reserve reconnaissance aircraft measured a peak 925-mb flight-level wind of 60 kt and an SFMR surface wind of 53 kt in very light rain. Since that time, deep convection has developed in the same area where those peak wind values were measured, so the initial intensity has been increased to a conservative 50 kt. Another recon aircraft is scheduled to investigate Michael around 0600 UTC. The initial motion estimate is northward, or 005/03 kt based on the recon and microwave satellite data. The bulk of the forecast rationale remains unchanged, although there remains some notable differences between the models that will ultimately determine where and when Michael will make landfall in about 72 h or so. The GFS, ECMWF, HWRF, and HMON models are tightly clustered along the western side of the guidance envelope. In contrast, the UKMET model is the farthest east of the dynamical models. Interestingly, the NOAA corrected-consensus HCCA model and the simple consensus IVCN models are close to each other and lie between the aforementioned model track dichotomy. Given that modest westerly vertical wind shear is expected to affect Michael throughout the forecast period until landfall occurs, which should keep the strongest convection, associated latent heat release, and pressure falls occurring in the eastern semicircle, the official forecast track leans more toward the HCCA/IVCN and UKMET model solutions. As a result, a slight eastward shift to the previous forecast track was made on this advisory through 48 hours, with little change made to the previous advisory track on days 3-5. Michael's overall cloud pattern remains unchanged, with the bulk of the convection being displaced into the eastern semicircle due to about 20 kt of westerly shear. However, the inner-core convective pattern within about 60 nmi of the center has been improving over the past few hours, and a recent SSMI/S microwave pass reveled a tightly curved band wrapping about 75 percent around the center. This better structure combined with very warm sea-surface temperatures of at least 29 deg C supports at least gradual strengthening until landfall despite the expected persistent westerly shear conditions. The HWRF model is the most robust of the intensity guidance and makes Michael a category 4 hurricane just prior to landfall. However, all of global models and the HWRF and HMON regional models are indicating westerly to west-northwesterly shear keeping the upper-level outflow restricted to the eastern semicircle, which is not a pattern conducive for the development of an intense hurricane. Therefore, the HRWF intensity solution has been discounted, and the new official intensity forecast remains similar to the previous advisory, which is close to but a little lower than the IVCN and ICON intensity consensus models. Although the 72-h forecast shows a decrease to 75 kt, this is due to the cyclone being inland, and should not be interpreted as being an indication of a weakening trend prior to landfall. Key Messages: 1. Michael is expected to produce heavy rainfall and flash flooding over portions of western Cuba and the northeastern Yucatan Peninsula of Mexico during the next couple of days. 2. Tropical storm conditions are expected tonight over portions of western Cuba and the northeastern Yucatan Peninsula, where tropical storm warnings are in effect. 3. Michael is forecast to be a hurricane when it reaches the northeastern Gulf Coast by mid-week, and the risk of dangerous storm surge, rainfall, and wind impacts continues to increase. In addition, Michael is expected to affect portions of the Florida Gulf Coast that are especially vulnerable to storm surge, regardless of the storm's exact track or intensity. Residents in these areas should monitor the progress of this system and follow any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 20.0N 85.4W 50 KT 60 MPH 12H 08/1200Z 21.1N 85.3W 60 KT 70 MPH 24H 09/0000Z 22.7N 85.6W 65 KT 75 MPH 36H 09/1200Z 24.4N 86.0W 75 KT 85 MPH 48H 10/0000Z 26.3N 86.1W 85 KT 100 MPH 72H 11/0000Z 30.4N 84.5W 75 KT 85 MPH...INLAND ERN FL PANHNDL 96H 12/0000Z 34.9N 78.4W 55 KT 65 MPH...INLAND 120H 13/0000Z 40.7N 64.4W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart
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