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Tropical Storm Nora Forecast Discussion Number 9
2021-08-27 22:49:02| National Hurricane Center (East Pacific)
Issued at 400 PM CDT Fri Aug 27 2021 000 WTPZ44 KNHC 272048 TCDEP4 Tropical Storm Nora Discussion Number 9 NWS National Hurricane Center Miami FL EP142021 400 PM CDT Fri Aug 27 2021 A 1656 UTC ASCAT-B scatterometer pass showed that Nora still does not have a tight inner core and instead has a 30-35 n mi region of winds 20 kt or less. However, the pass did show maximum wind vectors a little over 50 kt, so the storm has been strengthening, and maximum winds are estimated to be 55 kt. This is supported by Dvorak estimates of T3.5/55 kt from TAFB and SAB. A slight adjustment was made to Nora's initial position based on the scatterometer data, but the storm is still moving toward the northwest (310/10 kt). Nora is expected to maintain a motion toward the northwest or north-northwest as it heads in the direction of a weakness in the subtropical ridge which has developed over the U.S. southern Rockies and northern Mexico. The track guidance envelope appears to have tightened up compared to the past few days, with nearly all the model trackers showing Nora's center passing offshore just west of Cabo Corrientes, Mexico, in about 24 hours and then continuing northwestward either across the waters of the Gulf of California or inland over Baja California Sur. The new NHC track forecast has been nudged westward from this morning's forecast, but this is mainly due to the adjustment of the storm's initial position. This track is very close to the HCCA and other consensus aids. Nora's convective structure appears to be responding to a decrease in northeasterly shear, which is analyzed to be out of the northeast at 10-15 kt. This shear is forecast to decrease to 10 kt or less by tonight. Although Nora's broad structure could limit the storm's rate of strengthening, warm waters and upper-level divergence should allow it to become a hurricane over the next day or so. After that time, Nora's intensity will be strongly modulated on whether its center moves over mainland Mexico or the Baja California peninsula. If the center remains over water, as is shown in the official forecast, then environmental conditions appear conducive for Nora to remain as a hurricane for several more days, and the NHC forecast still closely follows the ECMWF-based SHIPS and LGEM models. That said, there is still greater-than- normal uncertainty in the intensity forecast after 48 hours. Key Messages: 1. Nora is forecast to strengthen to a hurricane on Saturday while passing nearby the coasts of the Mexican states of Jalisco and Nayarit, and hurricane watches and tropical storm warnings are in effect for portions of that coastline. Interests in these areas 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 Oaxaca, Guerrero, Michoacan, Colima, and Jalisco, as well as Baja California Sur. Life-threatening flash flooding and mudslides are expected. 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, it is still too soon to determine the magnitude and location of these potential impacts. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 15.5N 104.9W 55 KT 65 MPH 12H 28/0600Z 16.5N 105.6W 60 KT 70 MPH 24H 28/1800Z 18.3N 106.2W 65 KT 75 MPH 36H 29/0600Z 20.3N 107.0W 70 KT 80 MPH 48H 29/1800Z 21.9N 107.8W 75 KT 85 MPH 60H 30/0600Z 22.9N 108.6W 80 KT 90 MPH 72H 30/1800Z 23.9N 109.4W 80 KT 90 MPH 96H 31/1800Z 25.9N 110.9W 70 KT 80 MPH 120H 01/1800Z 28.4N 111.8W 55 KT 65 MPH $$ Forecaster Berg
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