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Hurricane Willa Forecast Discussion Number 9
2018-10-22 10:38:46| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Mon Oct 22 2018 000 WTPZ44 KNHC 220838 TCDEP4 Hurricane Willa Discussion Number 9 NWS National Hurricane Center Miami FL EP242018 300 AM MDT Mon Oct 22 2018 Willa is an impressive hurricane with rapid to explosive deepening having occurred over the past 48 hours, and yielding a 105-kt intensity increase during that time. Satellite intensity estimates range from subjective Dvorak T-numbers of T6.5/127 kt from TAFB and SAB to objective T-numbers of T7.0/140 kt from UW-CIMSS ADT and NHC. The most recent UW-CIMSS SATCON value around 0437Z was 127 kt. Based on these data and the slightly more ragged appearance of the CDO over the past couple of hours, the intensity is raised to 135 kt, which is just below category 5 strength. Willa is now moving northward and the initial motion estimate is 360/06 kt. Willa is forecast to continue moving northward today as the hurricane rounds the western portion of a deep-layer ridge located over central Mexico and which extends westward along 20N latitude to near the Pacific coast of Mexico. On Tuesday, a turn toward the north-northeast and northeast at a slightly faster forward speed is expected as the hurricane gets caught up in southwesterly flow ahead of an approaching mid-/upper-level trough. The latest 00Z NHC model guidance is in decent agreement on this general track scenario, but with noticeable differences in the forward speed. Internal statistical analyses show that the ECMWF and UKMET models have had a slow westward bias over the past 48 hours, which has significantly affected the consensus models. As a result, the new NHC forecast is a little to the right of and slightly faster the previous advisory track and the consensus models, and lies close to GFS model which has verified the best thus far. On the forecast track, Willa is expected to move over Las Islas Marias on Tuesday and then move inland over southwestern and west-central Mexico Tuesday night or early Wednesday. A 72-hour position has been provided only for continuity purposes beyond the 48-hour period, and Willa will likely have dissipated by then. Water temperatures ahead of the powerful hurricane are forecast to increase from 28 deg C to near 29.5 deg C, and the depth of the warm water is also expected to increase, which would tend to offset any cold upwelling beneath Willa. The deep-layer shear is forecast to increase to a little more than 10 kt during the next 36 hours, and remain at that level during the duration of that time period. These conditions would favor at least slight strengthening before the internal dynamics of the hurricane in the form of an eyewall replacement cycle (ERC) induces some weakening. With the eye diameter already at 10-15 nmi, an ERC could begin at any time during the next 12 hours. Shortly after 36 hours, the shear is expected to increase sharply to more than 20 kt, which will cause more significant weakening. However, Willa is still expected to be near major hurricane strength when it makes landfall along the west-central coast of Mexico. After landfall, the mountainous terrain along with strong southwesterly wind shear of more than 30 kt will cause rapid weakening and dissipation of the cyclone inland over north-central Mexico. Key Messages: 1. Willa is forecast to be a dangerous hurricane when it reaches the Islas Marias and the coast of southwestern Mexico by late Tuesday or Wednesday morning, bringing a life-threatening storm surge and flash flooding along with damaging hurricane-force winds. A Hurricane Warning is in effect for these areas, and residents should rush preparations to completion to protect life and property and follow any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 18.2N 107.1W 135 KT 155 MPH 12H 22/1800Z 19.2N 107.2W 135 KT 155 MPH 24H 23/0600Z 20.4N 107.2W 125 KT 145 MPH 36H 23/1800Z 21.8N 106.5W 115 KT 130 MPH 48H 24/0600Z 23.8N 104.6W 50 KT 60 MPH...INLAND WNCTRL MEXICO 72H 25/0600Z 27.0N 99.5W 20 KT 25 MPH...POST-TROP/INLAND 96H 26/0600Z...DISSIPATED INLAND $$ Forecaster Stewart
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