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Tropical Storm Miriam Forecast Discussion Number 7
2018-08-27 22:32:36| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Mon Aug 27 2018 553 WTPZ45 KNHC 272032 TCDEP5 Tropical Storm Miriam Discussion Number 7 NWS National Hurricane Center Miami FL EP152018 200 PM PDT Mon Aug 27 2018 Miriam has become a little better organized since the last advisory, and the convective banding has become better defined around the low-level center. However, this has not yet resulted in an increase of the various satellite intensity estimates, which remain mostly near 55 kt. Based on this, the initial intensity remains a possibly conservative 55 kt. Satellite imagery continues to indicate northwesterly to northerly vertical shear affecting Miriam, with cirrus clouds from the outer band to the north blowing into the central convection. The initial motion is 270/13. A large low- to mid-level ridge to the north of Miriam should continue to steer it westward for the next 36-48 h with some decrease in forward speed. After that, a large mid- to upper-level low to the northeast of the Hawaiian Islands is expected to cause the ridge to break between 140W-150W, with Miriam turning northwestward and north-northwestward in response. The track guidance is in good agreement on this scenario, but there remain some differences in Miriam's forward speed after recurvature between the faster ECMWF/UKMET and the slower GFS. The new forecast track is similar to the previous track through 72 h, then is nudged a little to the east based on an eastward shift in the consensus models. The global models continue to suggest a gradual increase in northwesterly shear over Miriam during the next day or so, followed by decreased shear from 24-48 h. There is some divergence in the intensity guidance through 72 h, with the SHIPS/LGEM models showing less strengthening than the HWRF/HMON/corrected consensus models. This part of the new intensity forecast is little changed from the previous forecast and lies between these two model camps. After 72 h, increasing southwesterly shear and cooler waters are expected to cause Miriam to weaken. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 14.0N 131.8W 55 KT 65 MPH 12H 28/0600Z 14.0N 133.5W 65 KT 75 MPH 24H 28/1800Z 13.9N 135.5W 70 KT 80 MPH 36H 29/0600Z 14.0N 137.5W 75 KT 85 MPH 48H 29/1800Z 14.5N 139.0W 85 KT 100 MPH 72H 30/1800Z 16.5N 141.0W 85 KT 100 MPH 96H 31/1800Z 20.0N 142.0W 75 KT 85 MPH 120H 01/1800Z 24.5N 143.5W 50 KT 60 MPH $$ Forecaster Beven
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