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Tropical Storm Nora Forecast Discussion Number 5
2021-08-26 22:38:06| National Hurricane Center (East Pacific)
Issued at 400 PM CDT Thu Aug 26 2021 000 WTPZ44 KNHC 262037 TCDEP4 Tropical Storm Nora Discussion Number 5 NWS National Hurricane Center Miami FL EP142021 400 PM CDT Thu Aug 26 2021 Scatterometer data from around midday showed that Nora has an expansive circulation with tropical-storm-force winds nearly reaching the coast of Mexico. The data also showed a possible center embedded within a larger area of light winds, but it is possible that there's another similar feature farther west where the instrument did not sample. Nora's winds remain 35 kt based on the ASCAT pass and the latest Dvorak fixes from TAFB and SAB, and the center has been placed between the two dumb-belling vorticity maxima. Even with the updated position, Nora is moving toward the west-northwest (285/8 kt), to the south of mid-level ridging over the southern United States. A shortwave trough currently over the northern Rockies is expected to erode the ridge over the next 12-24 hours, allowing Nora to turn toward the northwest and then north-northwest by the weekend. Even with the GFS's solution of multiple swirls consolidating over the next day or so, the 12Z run shifted left and now shows Nora potentially moving inland over Mexico farther west than it had in previous runs. A few of the other models--for example the HWRF and HMON--also bring the center inland as well, but the bulk of the interpolated model trackers continue to keep Nora just offshore but very near the coast of southwestern Mexico in about 48 hours. Model spread remains larger than normal, but no significant changes were required from the previous NHC track forecast based on the latest guidance suite. After passing southwestern Mexico, Nora is expected to be over Baja California Sur or the Gulf of California on days 4 and 5. Moderate northeasterly shear continues to affect Nora, but that shear is expected to decrease to a less-intrusive magnitude during the next 24 hours. Along with warm sea surface temperatures of 28-30 degrees Celsius, a moist mid-level environment, and upper-level divergence, Nora is expected to strengthen in the coming days. The rate of intensification could, however, be tempered by Nora's large size and structure. Assuming Nora does not move inland over southwestern Mexico, the storm is expected to become a hurricane on Saturday and then possibly continue strengthening up until the point it reaches the Baja California Peninsula. Much of the intensity guidance is based on scenarios showing Nora moving inland, which is suppressing the intensity consensus aids. Therefore, the NHC intensity forecast is mostly based on the ECMWF-based SHIPS and LGEM models, since the parent ECMWF model does not show Nora moving inland. Given Nora's larger wind field, tropical-storm-force winds are likely to reach the coast of Mexico earlier than expected. Therefore, the government of Mexico has issued a Tropical Storm Warning for a portion of the southwestern coast of Mexico. The Hurricane Watch issued earlier today also remains in effect. Key Messages: 1. Nora is forecast to strengthen to a hurricane by Saturday while it is near the coast of southwestern Mexico, and a hurricane watch and tropical storm warnings are in effect for portions of that area. Interests along the southwestern coast of Mexico should closely monitor the progress of this system and 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 a result, life-threatening flash flooding and mudslides could occur. 3. Nora is forecast to be near the southern portion of Baja California Sur as a hurricane early next week, bringing a risk of wind and rain impacts to that area. Given the above average uncertainty in the forecast, it is too soon to determine the magnitude and location of these potential impacts. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 13.4N 101.7W 35 KT 40 MPH 12H 27/0600Z 14.1N 102.7W 40 KT 45 MPH 24H 27/1800Z 15.3N 103.8W 50 KT 60 MPH 36H 28/0600Z 16.8N 104.7W 55 KT 65 MPH 48H 28/1800Z 18.6N 105.6W 65 KT 75 MPH 60H 29/0600Z 20.3N 106.7W 70 KT 80 MPH 72H 29/1800Z 21.6N 107.9W 75 KT 85 MPH 96H 30/1800Z 23.6N 110.0W 75 KT 85 MPH...OVER BAJA CAL SUR 120H 31/1800Z 25.2N 111.7W 55 KT 65 MPH...OVER BAJA CAL SUR $$ Forecaster Berg
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