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Tropical Depression GREG Forecast Discussion Number 34

2017-07-25 22:50:03| Tropical Depression LIDIA

Issued at 200 PM PDT Tue Jul 25 2017

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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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Hurricane Hilary Forecast Discussion Number 18

2017-07-25 22:42:31| National Hurricane Center (East Pacific)

Issued at 300 PM MDT Tue Jul 25 2017 000 WTPZ44 KNHC 252042 TCDEP4 Hurricane Hilary Discussion Number 18 NWS National Hurricane Center Miami FL EP092017 300 PM MDT Tue Jul 25 2017 Hilary continues to have a somewhat asymmetric presentation on the latest satellite imagery, with an eye feature in the northwestern portion of the central dense overcast, suggestive of some northwesterly shear. The initial wind speed remains 90 kt since there have been no significant changes to the satellite estimates. Higher wind shear is not far away from the hurricane, as evidenced by southward-moving cirrus clouds moving toward the center in the northern semicircle. Thus the window of time for Hilary to intensify may be closing, and little change in wind speed is shown for the next day or so. Afterward, gradually cooling SSTs, entrainment of drier air, and interaction with Hurricane Irwin is likely to cause more significant weakening. The NHC forecast is reduced from the previous one in the near term due to the shear, and at long range as Hilary probably moves over cold waters. This is not a particularly confident forecast at days 4-5 due to the interaction with Irwin. The initial motion estimate is the same as previous, 285/10 kt. A mid-tropospheric ridge extending westward from the southwestern United States should cause Hilary to continue on a west to west-northwestward track for the next several days. In a few days, however, Hilary is likely to pass close to Hurricane Irwin. While Irwin won't affect Hilary too much, the bulk of the guidance is showing Hilary slowing down and turning slightly left as Irwin pulls on Hilary's circulation. Model guidance has become more divergent after day 3, with the GFS indicating a northwestward motion due to the ridge weakening along 120-125W. The other guidance has been more consistent, so only small changes were made to the latest NHC forecast, which remains generally south and west of the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 15.5N 108.8W 90 KT 105 MPH 12H 26/0600Z 15.9N 110.5W 95 KT 110 MPH 24H 26/1800Z 16.4N 112.7W 95 KT 110 MPH 36H 27/0600Z 16.9N 114.8W 90 KT 105 MPH 48H 27/1800Z 17.5N 116.8W 85 KT 100 MPH 72H 28/1800Z 18.7N 120.4W 80 KT 90 MPH 96H 29/1800Z 19.7N 124.0W 70 KT 80 MPH 120H 30/1800Z 20.5N 127.5W 50 KT 60 MPH $$ Forecaster Blake

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Tropical Storm GREG Forecast Discussion Number 33

2017-07-25 16:50:29| Tropical Depression LIDIA

Issued at 800 AM PDT Tue Jul 25 2017

Tags: number discussion storm tropical

 

Hurricane HILARY Forecast Discussion Number 17

2017-07-25 16:39:30| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Tue Jul 25 2017 000 WTPZ44 KNHC 251439 TCDEP4 Hurricane Hilary Discussion Number 17 NWS National Hurricane Center Miami FL EP092017 900 AM MDT Tue Jul 25 2017 Satellite imagery shows that deep, but somewhat asymmetric, convection continues in the inner core of Hilary. The 1-minute visible imagery from GOES-16 indicates strong convective towers are firing in the northeastern eyewall, then attempting to rotate cyclonically around the center. Still, the eyewall remains open in the southwest quadrant, as suggested in the visible imagery and shown in a recent 1340 UTC SSMIS microwave pass. Intensity estimates remain about the same as overnight, so the initial wind speed will stay at 90 kt. Hilary is forecast to remain in a conducive environment for strengthening during the next day or so. However, the northerly wind shear is not far away, as evidenced by cirrus clouds moving toward the center in the northern semicircle, which could cause the hurricane to level off in intensity. Similar to yesterday at this time, the model guidance has really backed down off the peak intensity, with few of the solutions even showing Hilary reaching 100 kt. It was easier to ignore the models yesterday because they seemed unrealistic; today the shear is approaching and should impact the cyclone within 24 hours. It seems best to only gradually reduce the intensity forecast, so the latest NHC prediction is adjusted toward the model consensus by day 3, when more significant weakening is expected due to cooler waters, drier air, and interaction with Hurricane Irwin. The initial motion estimate is a little to the left and faster, 285/10 kt. A mid-tropospheric ridge extending westward from the southwestern United States should cause Hilary to continue on a west to west-northwestward track for the next several days. In a few days, however, Hilary is likely to pass close to Hurricane Irwin. While Irwin won't affect Hilary too much, the bulk of the guidance is showing a slowdown and slight turn to the left of Hilary as Irwin tugs on its circulation. Overall, models are in fairly good agreement considering the complexity of the situation, with even most of the GFS-based guidance now acknowledging the binary interaction. The official forecast has been gradually shifting westward at long range, and this advisory continues that trend, near or just west of the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 15.3N 107.8W 90 KT 105 MPH 12H 26/0000Z 15.8N 109.5W 100 KT 115 MPH 24H 26/1200Z 16.3N 111.7W 100 KT 115 MPH 36H 27/0000Z 16.8N 113.9W 100 KT 115 MPH 48H 27/1200Z 17.4N 116.0W 95 KT 110 MPH 72H 28/1200Z 18.5N 120.0W 80 KT 90 MPH 96H 29/1200Z 19.5N 124.0W 70 KT 80 MPH 120H 30/1200Z 20.0N 127.5W 60 KT 70 MPH $$ Forecaster Blake

Tags: number discussion forecast hurricane

 

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