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Hurricane DARBY Forecast Discussion Number 20
2016-07-16 16:47:40| National Hurricane Center (East Pacific)
Issued at 800 AM PDT SAT JUL 16 2016 000 WTPZ45 KNHC 161447 TCDEP5 HURRICANE DARBY DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 800 AM PDT SAT JUL 16 2016 Darby continues to have a well-defined 20 n mi wide eye, which is completely encircled by convective cloud tops as cold as -70C. Satellite intensity estimates at 1200 UTC were rather conflicting. Subjective Dvorak numbers increased from six hours ago, but at the same time objective ADT estimates have decreased. Given this discrepancy, the initial intensity is kept at 90 kt. Darby is beginning to move over cooler water, with the eye having reached the 26C isotherm. Although vertical shear over the cyclone is expected to be low for the next few days, SSTs will be dropping to as cold as 23C by 72 hours. Therefore, gradual weakening is anticipated to begin soon, with Darby likely becoming a tropical storm in about 48 hours. Increasing shear should then contribute to a faster weakening rate after 48 hours. The new NHC intensity forecast is very close to the IVCN intensity consensus during the entire forecast period, and it is a little lower than the previous forecast from 36 hours and beyond. The initial motion is west-northwestward, or 290/9 kt. The subtropical ridge to the north of Darby is in the process of weakening due to an amplifying trough along the west coast of the United States. Therefore, Darby is expected to continue moving west-northwestward for the next 24 hours. After that time, the weakening cyclone will come under the influence of lower-level steering, causing it to move westward through the end of the forecast period. There is very little spread among the track models, and the NHC track forecast is just an update of the previous one. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 17.8N 123.9W 90 KT 105 MPH 12H 17/0000Z 18.2N 125.1W 85 KT 100 MPH 24H 17/1200Z 18.6N 126.8W 75 KT 85 MPH 36H 18/0000Z 18.9N 128.7W 65 KT 75 MPH 48H 18/1200Z 19.1N 130.7W 60 KT 70 MPH 72H 19/1200Z 19.7N 135.2W 50 KT 60 MPH 96H 20/1200Z 19.9N 140.0W 40 KT 45 MPH 120H 21/1200Z 19.0N 145.0W 35 KT 40 MPH $$ Forecaster Berg
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