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Tropical Storm Miriam Forecast Discussion Number 10
2018-08-28 16:56:12| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Tue Aug 28 2018 674 WTPZ45 KNHC 281456 TCDEP5 Tropical Storm Miriam Discussion Number 10 NWS National Hurricane Center Miami FL EP152018 800 AM PDT Tue Aug 28 2018 A very recently arriving high-resolution microwave overpass indicates that Miriam is a sheared tropical cyclone. The GPM pass shows that the center of Miriam is located well northwest of the primary mass of deep convection due to moderate northwesterly shear. The center of the cyclone is located well west of the earlier position estimates, which has also required a re-location. The most recent Dvorak estimates from TAFB and SAB, as well as UW-CIMSS/ADT, support an initial intensity, however, this could be generous given the recent microwave data. Environmental conditions are not expected to change over the next 24 hours, with possibly a slight reduction in the shear in 24 to 48 hours. This would suggest that Miriam should only gradually strengthen over the next couple of days and it is likely to reach its peak intensity in 2-3 days. After that time, increasing southwesterly shear and cooler waters are expected to initiate weakening. By 96 hours, the shear is forecast to become quite strong and Miriam will be moving over sub 26C SSTs. These progressively hostile conditions should cause Miriam to become a post-tropical cyclone by 120 hours. The latest intensity forecast is close to the FSU Superensemble, and generally in between the ICON and HCCA consensus models. The initial motion continues to be due westward, or 270/12 kt, as Miriam continues to be steered around the southern periphery of a subtropical ridge. A mid- to upper-level trough northeast of Hawaii will weaken the western periphery of the ridge over the next couple of days, and Miriam is forecast to turn northwest then north-northwest, between the ridge and the aforementioned trough. Forecast models diverge regarding the forward speed of Miriam at days 3-5, depending how they handle the interaction of Miriam with the the trough to its northwest. The ECMWF continues to favor an accelerating northward track as Miriam gets caught in strong southerly flow on the eastern side of the trough. The GFS is much farther southwestward, as it appears to take a more shallow Miriam westward later in the forecast period. Since the consensus aids remain clustered between these two scenarios, the latest forecast NHC track is once again near the various consensus models. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 14.2N 135.4W 55 KT 65 MPH 12H 29/0000Z 14.2N 136.9W 55 KT 65 MPH 24H 29/1200Z 14.3N 138.9W 60 KT 70 MPH 36H 30/0000Z 14.7N 140.4W 65 KT 75 MPH 48H 30/1200Z 15.6N 141.3W 75 KT 85 MPH 72H 31/1200Z 18.5N 141.8W 75 KT 85 MPH 96H 01/1200Z 22.0N 142.6W 50 KT 60 MPH 120H 02/1200Z 26.0N 144.8W 35 KT 40 MPH...POST-TROPICAL $$ Forecaster Brown/Latto
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