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Hurricane Nora Forecast Discussion Number 11
2021-08-28 11:00:40| National Hurricane Center (East Pacific)
Issued at 400 AM CDT Sat Aug 28 2021 000 WTPZ44 KNHC 280900 TCDEP4 Hurricane Nora Discussion Number 11 NWS National Hurricane Center Miami FL EP142021 400 AM CDT Sat Aug 28 2021 The inner-core structure appears to be tightening up with Nora this morning. Deep convection with tops colder than -70 C has been blossoming and wrapping around the center, first around the eastern side, but more recently in all quadrants as a distinct warm spot denotes the center. Earlier, there was a helpful SSMIS microwave pass at 0143 UTC that showed a closed cyan ring on the 37 GHz channel, which is a signal often related to a formative low-level eyewall and is often a harbinger for significant intensification. An ASCAT-B pass at 0403 UTC also suggested the wind-radii were gradually contracting, and also that the center position is a little further east of the short-term track. The latest subjective Dvorak estimates at 0600 UTC from SAB and TAFB have both increased to T4.0/65 kt. These estimates, in addition to the recent structural improvements in IR satellite and microwave imagery, support raising the intensity to 65-kt for this advisory, making Nora a hurricane. Nora continues to move a little more poleward this morning, with the latest motion estimate at 345 degrees at 9 kt. While the track forecast philosophy hasn't changed much over the last day, as a weakening mid-level ridge provides a weakness for Nora to escape north-northwestward, there has been a notable eastward shift in the track guidance. The deterministic ECMWF run, for instance, is now showing the hurricane brushing the shoreline of Mainland Mexico near Cabo Corrientes in 24 hours, and is now quite similar to the latest GFS forecast. The ECMWF ensembles have also shifted further east, with around half of the members explicitly showing landfall over mainland Mexico. The latest NHC track forecast has thus been shifted eastward, especially during the first 24-48 hours of the forecast, but I did not want to shift Nora's track as far east as the latest HCCA and TVCE consensus aids and further eastward adjustments may be necessary in subsequent forecasts. Afterwards, if Nora remains intact, the guidance shows the system bending back to the northwest and running up the gap of the Gulf of California between Baja California Sur and Mainland Mexico. Now that Nora appears to developing an inner core, at least steady intensification is expected in the short-term while the hurricane remains far enough offshore of mainland Mexico in a favorable dynamic and thermodynamic environment. After 12 hours, the intensity forecast becomes very tricky, due to just how much land interaction Nora will encounter as it brushes by Mexico. Once again, a lot of the reliable intensity guidance shows substantial land interaction and are sharply lower after 24 hours. Because the latest forecast track has been shifted further east, it increases the chance that significant disruption of the storm may occur by the mountainous terrain located near the coast of Mexico in that location. The latest intensity forecast was lowered after 24 hours and held at 70 kt through 96 hours due to this large uncertainty tied to possible land interaction. The latest forecast remains higher than the majority of the guidance, but is lower than the previous forecast. The wind radii have also been adjusted smaller after 24 hours, as the global model guidance suggests that the TC wind field will shrink quite dramatically as the system tracks near mainland Mexico. Tropical Storm and Hurricane Warnings have been extended further north along the mainland Mexico coastline given the eastward adjustments in the latest forecast track. Key Messages: 1. Nora is forecast strengthen today as it approaches the coasts of the Mexican states of Jalisco and Nayarit, and hurricane warnings are in effect for portions of that coastline. Interests in these areas and points further north should closely monitor the progress of Nora and subsequent updates to the forecast. 2.Heavy rain associated with Nora is expected across coastal sections of the Mexican states of Guerrero, Michoacan, Colima, Jalisco and Nayarit, as well as Baja California Sur. Life-threatening flash flooding and mudslides are expected. As Nora lifts northwest, heavy rainfall will spread into the Mexican states of Sinaloa and Sonora as well as the southwestern U.S. during the middle to latter portion of next week. 3. Nora is forecast to move over the Gulf of California as a hurricane early next week, bringing a risk of wind and rain impacts to portions of the Mexican states of Baja California Sur, Sinaloa, and Sonora. Given the above-average uncertainty in the forecast intensity, confidence is not high enough to determine the magnitude and location of these potential impacts. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 17.1N 105.2W 65 KT 75 MPH 12H 28/1800Z 18.8N 105.5W 75 KT 85 MPH 24H 29/0600Z 20.8N 106.1W 75 KT 85 MPH...NEAR MAINLAND MEXICO 36H 29/1800Z 22.4N 107.0W 70 KT 80 MPH 48H 30/0600Z 23.3N 107.8W 70 KT 80 MPH 60H 30/1800Z 24.1N 108.6W 70 KT 80 MPH 72H 31/0600Z 24.9N 109.4W 70 KT 80 MPH 96H 01/0600Z 26.4N 110.6W 70 KT 80 MPH 120H 02/0600Z 28.7N 111.0W 45 KT 50 MPH...INLAND $$ Forecaster Papin/Beven
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