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Hurricane Norman Forecast Discussion Number 15
2018-08-31 22:34:32| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Fri Aug 31 2018 824 WTPZ41 KNHC 312034 TCDEP1 Hurricane Norman Discussion Number 15 NWS National Hurricane Center Miami FL EP162018 200 PM PDT Fri Aug 31 2018 Satellite derived mid and upper tropospheric winds and the UW-CIMSS shear analysis indicate that the persistent northeasterly vertical shear has increased to 20-25 kt, and has continued to impede outer deep convective banding development in the northern portion of Norman's inner core. The cloud pattern has also become somewhat asymmetric (northeast to southwest). A series of recent microwave images, however, show that the eyewall is now closed, although the eye temperature has warmed a bit during the past 6 hours. The Dvorak satellite intensity classifications from TAFB and SAB also support these observations, and the initial intensity is reduced to 110 kt. Although there may still be some fluctuations in intensity, gradual weakening is forecast through day 5, primarily due to the shear predicted by the GFS and ECMWF Decay-SHIPS intensity models. Intrusion of stable air mass, beyond day 3, northeast of the Hawaiian Islands will also promote this weakening trend. The official intensity forecast has changed little from the previous advisory, and is still based on the HFIP Corrected Consensus Approach and IVCN intensity models. The initial motion is estimated to be west-southwest, or 255/7 kt. An anchored mid- to upper-level ridge that stretches west-southwestward from the Baja California peninsula should steer Norman west-southwestward during the next 12 hours or so. Afterward, the southwestern-most segment of the ridge axis between Miriam and Norman weakens as Miriam continues on a northward track. This change in the synoptic steering pattern should influence Norman to turn back toward the west or west-northwest by early next week. Only slight along-track speed adjustments were made to this advisory, which follows a blend of the HCCA and TVCN consensus guidance. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 16.5N 121.5W 110 KT 125 MPH 12H 01/0600Z 16.2N 122.6W 100 KT 115 MPH 24H 01/1800Z 16.2N 124.4W 95 KT 110 MPH 36H 02/0600Z 16.6N 127.0W 90 KT 105 MPH 48H 02/1800Z 17.3N 129.9W 85 KT 100 MPH 72H 03/1800Z 18.9N 136.0W 80 KT 90 MPH 96H 04/1800Z 20.0N 141.1W 70 KT 80 MPH 120H 05/1800Z 20.9N 144.7W 65 KT 75 MPH $$ Forecaster Roberts
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