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Hurricane Norman Forecast Discussion Number 18
2018-09-01 16:54:39| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Sat Sep 01 2018 734 WTPZ41 KNHC 011454 TCDEP1 Hurricane Norman Discussion Number 18 NWS National Hurricane Center Miami FL EP162018 800 AM PDT Sat Sep 01 2018 Although satellite intensity estimates indicate that Norman has continued to weaken, the weakening trend appears to have abated. This is based on recent infrared imagery showing a better developed CDO feature accompanied by improved outflow, and also a well-defined closed eye now depicted in a 1148Z AMSR and 1158Z SSMIS microwave satellite images. The initial intensity has been lowered to 90 kt, which is a blend of the various satellite intensity estimates, with a little more weight placed on the TAFB estimate of T5.0/90 kt. Norman's initial motion estimate is 270/10 kt. The aforementioned eye noted in the microwave passes greatly helped with determining the cyclone's location and past motion. Other than some slight forward speed adjustments made in the first 24 hours due to the faster initial motion, no significant changes were required to the previous track forecast. Norman is forecast to move westward to west-northwestward for the next several days as the hurricane moves along the southern periphery of strong deep-layer ridge to the north. The models are in excellent agreement on the track of Norman through 72 h, and then diverge noticeably after that time with the GFS taking Norman more westward in the general direction of the Hawaiian Islands, whereas the ECMWF, HWRF, and HMON models keep Norman well to the northeast of the islands. The official forecast track lies close to the middle of the tightly packed guidance envelope through 72 h, and then is close to the consensus aids HCCA and FSSE after that. The shear that has been affecting Norman appears to have weakened some this morning, and that decreasing trend is expected to continue throughout the forecast period, becoming near zero in 48-72 h according to the ECMWF model. The GFS model shows a similar decreasing shear trend, but just not as much as the ECMWF model. The HWRF and HMON models also have the shear decreasing and do a complete reversal by re-strengthening Norman into a major hurricane again during the next 24 h, followed by slow weakening thereafter. For now, the official intensity forecast shows little change in strength for the next 24 h, followed by slow weakening during the remainder of the forecast period as the cyclone encounters drier air and cooler sea-surface temperatures near 26C. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 16.2N 123.7W 90 KT 105 MPH 12H 02/0000Z 16.3N 125.4W 90 KT 105 MPH 24H 02/1200Z 16.9N 128.2W 90 KT 105 MPH 36H 03/0000Z 17.8N 131.3W 85 KT 100 MPH 48H 03/1200Z 18.7N 134.6W 85 KT 100 MPH 72H 04/1200Z 20.3N 140.6W 70 KT 80 MPH 96H 05/1200Z 21.3N 145.3W 65 KT 75 MPH 120H 06/1200Z 22.0N 148.6W 60 KT 70 MPH $$ Forecaster Stewart
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