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Tropical Storm Olaf Forecast Discussion Number 7
2021-09-09 10:55:31| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Thu Sep 09 2021 000 WTPZ45 KNHC 090855 TCDEP5 Tropical Storm Olaf Discussion Number 7 NWS National Hurricane Center Miami FL EP152021 300 AM MDT Thu Sep 09 2021 Olaf's convective canopy has been expanding somewhat and become a little more circular since last evening with clouds tops as cold as -80 degrees Celsius. Dvorak estimates have bounced up to T3.5 from TAFB, SAB, and the UW-CIMSS ADT, and Olaf's maximum winds are therefore now estimated to be 55 kt. Recent scatterometer data also indicated that the tropical-storm-force wind field is a little bigger than previously estimated. Also with the help of the scatterometer data, Olaf's center appears to have tracked a bit to the east, and the initial motion is estimated to be north-northwestward, or 340/5 kt. This has been the recent trend over the past day or so, with the motion having a more northward component than anticipated--but not surprising given what previous GFS model runs have been suggesting. A strong mid-level high over the western United States is expected to eventually force Olaf toward the northwest and then west, but probably not soon enough to avoid impacts on the southern Baja California peninsula. Mostly due to the adjusted initial position, the track models--and the NHC official forecast--have again shifted closer to the southern tip of the peninsula, with a closest approach in about 24 hours. This updated forecast is very close to the HCCA consensus aid and would be close enough for the core of the storm to at least graze land. It's also concerning that the GFS, HMON, and COAMPS-TC models are still to the right of the official forecast and the other models and show Olaf's center potentially moving over the southern tip of the peninsula in about 24 hours. Olaf should finally begin to move westward away from the peninsula in about 48 hours. Although satellite images and model analyses suggest that some moderate westerly shear is undercutting the outflow layer, Olaf has been able to strengthen nonetheless. If Olaf's center does not move over the Baja California peninsula, the storm will have the opportunity to strengthen for another 24-36 hours while ocean waters are warm and deep-layer shear is low. Therefore, the new NHC intensity forecast is near the upper end of the guidance envelope and shows Olaf becoming a hurricane later today. Further strengthening beyond what's shown in the official forecast is possible, with rapid intensification indices now close to a 50 percent chance of a 25-kt increase in winds over the next 24 hours. By 48 hours, colder waters should cause Olaf's convection to decrease, and global models suggest it could degenerate to a convection-less post-tropical low by day 3. The updated track and intensity forecasts have necessitated the issuance of a Hurricane Warning by the government of Mexico for southern portions of Baja California Sur, and an extension of Tropical Storm Warnings northward along both east and west coasts of the peninsula. Key Messages: 1. Olaf is forecast to strengthen to a hurricane later today and then pass very near or over the southern portion of Baja California Sur tonight and on Friday. Tropical storm conditions are expected to begin within the hurricane warning area this afternoon, and preparations should therefore be rushed to completion this morning. 2. Heavy rains associated with Olaf are possible across portions of far southern Baja California Sur today through Friday. This will pose a threat of flash flooding and mudslides. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 20.5N 108.0W 55 KT 65 MPH 12H 09/1800Z 21.4N 108.6W 65 KT 75 MPH 24H 10/0600Z 22.6N 110.0W 70 KT 80 MPH 36H 10/1800Z 23.5N 111.7W 65 KT 75 MPH 48H 11/0600Z 23.7N 113.2W 50 KT 60 MPH 60H 11/1800Z 23.5N 114.5W 40 KT 45 MPH 72H 12/0600Z 23.1N 115.7W 35 KT 40 MPH...POST-TROPICAL 96H 13/0600Z 22.1N 118.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 14/0600Z 21.3N 121.7W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg
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