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Hurricane Hilary Forecast Discussion Number 19
2017-07-26 04:50:03| National Hurricane Center (East Pacific)
Issued at 900 PM MDT Tue Jul 25 2017 000 WTPZ44 KNHC 260249 TCDEP4 Hurricane Hilary Discussion Number 19 NWS National Hurricane Center Miami FL EP092017 900 PM MDT Tue Jul 25 2017 Hilary's convective cloud pattern has continued to fluctuate between an occasional symmetric appearance containing a cloud-covered eye to the current asymmetric pattern with little or no outer banding features evident and the eye completely obscured in conventional infrared imagery. However, recent SSMI, SSMIS, and AMSU microwave images still indicate that Hilary has a well-defined, 10-nmi-diameter eye and a thick eyewall beneath the cirrus canopy. Satellite intensity estimates range from T4.5/77 kt and T5.0/90 kt from TAFB and SAB, respectively, to T5.5/102 kt from the NHC Dvorak objective technique. Given the large range of estimates, the initial intensity will remain at 90 kt for now, which could be a little conservative. The initial motion remains a steady 285/10 kt. Hilary is forecast to continue on a general west-northwestward track for the next 72 hours or so. Thereafter, a slight bend toward the west with a decrease in forward speed is expected due to binary/Fujiwhara interaction with Hurricane Irwin. The forward speed difference between Hilary and Irwin is about 3-4 kt, with Hilary steadily getting closer to Irwin. That trend should continue on days 4 and 5 with the distance between the two cyclones decreasing to about 300 nmi, resulting in the two systems orbiting cyclonically about each other. Since Hilary is forecast to be the larger and more dominant circulation, Irwin's effect on Hilary's track is expected to be minimal. The latest NHC model guidance remains tightly clustered around the previous advisory track, so the new track forecast is just an extension of the previous advisory. Although SHIPS and UW-CIMMS shear analyses indicate north to northwesterly vertical wind shear of about 15 kt, there is no evidence of this shear based on water vapor imagery showing nearly symmetrical cirrus outflow and the eye being embedded in the center or south side of the CDO. The main inhibiting factor that has kept Hilary from strengthening appears to have been intermittent dry air intrusions into the inner-core region causing a brief erosion of the eyewall convection. Microwave data suggests that dry air remains nearby, so little if any intensification is forecast for the next 24 hours as a result. By 36 h and beyond, Hilary will be moving over sub-26C SSTs and upper-ocean heat content values near zero, and reaching 24C water on days 4 and 5. The decreasing thermodynamics should result in gradual weakening from 36-72 hours, with faster weakening thereafter. The new NHC intensity forecast closely follows the previous advisory and the IVCN intensity consensus model. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 16.0N 109.8W 90 KT 105 MPH 12H 26/1200Z 16.4N 111.5W 95 KT 110 MPH 24H 27/0000Z 16.9N 113.6W 90 KT 105 MPH 36H 27/1200Z 17.4N 115.7W 85 KT 100 MPH 48H 28/0000Z 18.0N 117.5W 80 KT 90 MPH 72H 29/0000Z 19.2N 121.1W 75 KT 85 MPH 96H 30/0000Z 20.0N 124.8W 60 KT 70 MPH 120H 31/0000Z 21.0N 128.3W 45 KT 50 MPH $$ Forecaster Stewart
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