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Tropical Storm Miriam Forecast Discussion Number 4
2018-08-27 04:44:01| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Sun Aug 26 2018 372 WTPZ45 KNHC 270243 TCDEP5 Tropical Storm Miriam Discussion Number 4 NWS National Hurricane Center Miami FL EP152018 800 PM PDT Sun Aug 26 2018 The overall cloud pattern of Miriam has continued to gradually improve this evening. However, light northerly shear of about 10 kt, as analyzed by UW-CIMSS, seems to be preventing the cyclone from strengthening at a more rapid pace. Earlier ASCAT data and a more recent partial AMSR overpass indicated that the low-level center of Miriam is slightly displaced to the northwest of most of the deep convection, but is still well-embedded within the cirrus canopy. A consensus of objective and subjective satellite intensity estimates suggests that Miriam has strengthened a little since the last advisory, so the initial intensity has been increased to 45 kt. The tropical storm is still moving westward at around 12 kt, and all indications are that this motion will continue for the next few days. By day 4, Miriam should turn northward as it reaches a break in the subtropical ridge created by an extensive mid- to upper-level low located over the central North Pacific. The track guidance is in good agreement on this general scenario, but still differs on the exact timing and location of the northward turn. The NHC forecast therefore remains near the middle of the guidance envelope, and is essentially a blend of the HCCA and TVCX consensus aids and the previous forecast. Steady strengthening is still likely for the next day or two. While Miriam's structure does not appear to be conducive for rapid intensification at the moment, this could change quickly and with little warning due to the small size of the cyclone's inner-core. The model spread increases from 36 h onward, with the dynamical models indicating continued intensification to major hurricane strength, while the statistical guidance is much lower. Regardless of Miriam's peak intensity, by the end of the forecast, steady weakening is likely as Miriam encounters lower SSTs and higher shear. The NHC forecast continues to favor the higher dynamical models for the first couple of days, and closely follows the intensity consensus after that. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 13.8N 127.9W 45 KT 50 MPH 12H 27/1200Z 13.9N 129.7W 55 KT 65 MPH 24H 28/0000Z 13.7N 131.9W 65 KT 75 MPH 36H 28/1200Z 13.8N 134.0W 80 KT 90 MPH 48H 29/0000Z 13.9N 136.0W 90 KT 105 MPH 72H 30/0000Z 14.3N 139.5W 90 KT 105 MPH 96H 31/0000Z 16.8N 141.3W 80 KT 90 MPH 120H 01/0000Z 21.0N 141.5W 65 KT 75 MPH $$ Forecaster Zelinsky
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