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Tropical Storm Miriam Forecast Discussion Number 8
2018-08-28 04:35:10| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Mon Aug 27 2018 917 WTPZ45 KNHC 280235 TCDEP5 Tropical Storm Miriam Discussion Number 8 NWS National Hurricane Center Miami FL EP152018 800 PM PDT Mon Aug 27 2018 Miriam hasn't changed much over the past several hours. Last-light visible imagery and a couple of microwave overpasses around 0000 UTC show that the tropical storm remains lightly sheared from the northwest. Although outflow from the deepest inner-core convection seems to have become better established, cloud tops from outer bands to the north and east are still moving toward the center of the cyclone, indicating there is still shear below the outflow layer. The initial intensity has been held at 55 kt, in agreement with nearly all of the objective and subjective satellite estimates. Miriam continues to move westward, and the forward speed is now 10 kt. The guidance remains in very good agreement on the track of Miriam for the next 36 hours, with only slight speed differences between the various models. Beyond that time, the tropical storm should begin to turn north-northwestward toward a break in the subtropical ridge created by a mid- to upper-level trough over the central Pacific. The model spread increases drastically at this point, with the ECMWF showing a quicker turn and a faster north-northwestward motion than the GFS, with most of the other guidance in between. For now, the NHC forecast has not been significantly changed, and remains near the corrected consensus, HCCA. The moderate shear currently affecting Miriam is forecast by the global models to continue for the next 24 h or so, preventing the cyclone from strengthening significantly. Between 24 and 72 h, this shear is forecast to decrease, allowing the cyclone to strengthen at a quicker rate. By the end of the forecast period, Miriam should quickly weaken as it encounters higher shear and cooler SSTs. The HWRF is a notable outlier, showing much faster intensification, but it is possible this model is not properly representing the shear currently affecting Miriam. That said, if the shear decreases sooner than expected, it is possible that Miriam could intensify much faster than currently anticipated. The new NHC intensity forecast is close to the intensity consensus, and shows a slightly slower initial intensification rate for Miriam, and a faster decay by day 5, than the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 14.0N 132.5W 55 KT 65 MPH 12H 28/1200Z 14.0N 134.1W 60 KT 70 MPH 24H 29/0000Z 14.0N 136.2W 65 KT 75 MPH 36H 29/1200Z 14.2N 138.1W 75 KT 85 MPH 48H 30/0000Z 15.0N 139.5W 85 KT 100 MPH 72H 31/0000Z 17.5N 141.1W 85 KT 100 MPH 96H 01/0000Z 21.5N 142.0W 65 KT 75 MPH 120H 02/0000Z 26.0N 144.0W 40 KT 45 MPH $$ Forecaster Zelinsky
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