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Hurricane Irwin Forecast Discussion Number 14
2017-07-25 22:44:00| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Tue Jul 25 2017 000 WTPZ45 KNHC 252043 TCDEP5 Hurricane Irwin Discussion Number 14 NWS National Hurricane Center Miami FL EP102017 200 PM PDT Tue Jul 25 2017 Irwin's satellite presentation has improved since the last advisory, with a well-defined eye showing up in infrared imagery, and an elongated band extending around the western and northern side of the circulation. Using the eye pattern from the Dvorak technique yields an estimate of T4.5/77 kt, so the initial intensity is raised to 75 kt. Irwin has already strengthened beyond what we were originally forecasting, so it's a little difficult to know if it will intensify further. However, 10-15 kt of southerly shear is expected to remain over the cyclone for the next 24 hours, and the hurricane's slow motion could cause some upwelling of colder water. Therefore, gradual weakening is forecast during the next 48 hours. After that time, Irwin will begin interacting with Hurricane Hilary, and since it has the smaller circulation of the two, it is likely to suffer and be the one that loses intensity. Water temperatures also cool significantly as Irwin accelerates toward the north, so more definitive weakening is expected by the end of the forecast period. Some of the global models show Irwin becoming absorbed into Hilary's circulation before the end of the forecast period, so it's possible that dissipation could occur by day 5. Irwin continues to move generally westward, but that motion is likely to become more west-southwestward from 12-48 hours as Hilary approaches from the east. The Fujiwhara interaction with Hilary will then cause Irwin to stall around day 3, and then accelerate around the southeast and then northeast side of Hilary on days 4 and 5. Although the track models all agree on this general scenario, there remain a large amount of spread regarding when and where Irwin will turn toward the north. To be conservative, the updated NHC track forecast is near the middle of the guidance envelope, close to the previous forecast but also to the right of the TVCN multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 15.7N 120.1W 75 KT 85 MPH 12H 26/0600Z 15.3N 121.0W 70 KT 80 MPH 24H 26/1800Z 14.8N 122.1W 65 KT 75 MPH 36H 27/0600Z 14.4N 123.1W 60 KT 70 MPH 48H 27/1800Z 14.3N 123.6W 55 KT 65 MPH 72H 28/1800Z 14.7N 123.4W 55 KT 65 MPH 96H 29/1800Z 17.5N 123.0W 55 KT 65 MPH 120H 30/1800Z 21.5N 125.5W 45 KT 50 MPH $$ Forecaster Berg
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