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Tropical Storm Olaf Forecast Discussion Number 12
2021-09-10 16:51:00| National Hurricane Center (East Pacific)
Issued at 900 AM MDT Fri Sep 10 2021 000 WTPZ45 KNHC 101450 TCDEP5 Tropical Storm Olaf Discussion Number 12 NWS National Hurricane Center Miami FL EP152021 900 AM MDT Fri Sep 10 2021 The satellite presentation of Olaf has significantly degraded over the past several hours after the center moved across the southern portion of Baja California Sur overnight. The system's organized convection has collapsed, and infrared satellite imagery indicates cloud top temperatures are rapidly warming near the estimated center position. The initial intensity is lowered to 60 kt for this advisory, which now makes Olaf a tropical storm. This estimate may still be generous, but limited surface observations and radar data make it difficult to confidently assess the intensity. Hopefully, scatterometer data this afternoon will provide more insight into changes in Olaf's surface wind field. The tropical storm has slowed down a bit since last night, and its estimated motion is northwest (310 degrees) at 9 kt. Recent microwave imagery suggests the center of Olaf is just offshore the southwestern coast of Baja California Sur, and the cyclone is likely to move roughly parallel to the coast today. Then, a strong mid-level high pressure ridge centered over the southern Rockies is expected to build westward to the north of Olaf. This ridge should turn Olaf toward the west by tonight, and then toward the southwest through early next week. The official NHC track forecast has been adjusted to the south of the previous forecast once again, in agreement with the latest multi-model consensus aids. Olaf is likely to continue rapidly weakening during the next couple of days. In the short-term, its proximity to the mountainous terrain of the Baja California peninsula will disrupt its ability to sustain organized convection. As Olaf moves away from land, the cyclone will encounter decreasing sea-surface temperatures and very dry mid-level air, which should expedite its transition into a post-tropical cyclone. In fact, the latest GFS and ECMWF model simulated satellite imagery show Olaf becoming completely devoid of convection within the next 24-36 h. The latest NHC intensity forecast shows more rapid weakening than the previous one, primarily based on recent satellite trends and the lower initial intensity. The official forecast remains below the HCCA and IVCN consensus aids, which are inflated by the SHIPS and LGEM models that fail to weaken Olaf during the next 24 h. Key Messages: 1. Olaf is forecast to move along the southwestern coast of the Baja California peninsula today, with tropical storm conditions continuing over southern portions of Baja California Sur through this evening. These winds should diminish tonight as Olaf continues weakening and turns westward away from land. 2. Heavy rains associated with Olaf are expected across portions of southern Baja California Sur through today. This will pose a threat of significant and life-threatening flash flooding and mudslides. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 24.1N 111.3W 60 KT 70 MPH 12H 11/0000Z 24.5N 112.4W 50 KT 60 MPH 24H 11/1200Z 24.6N 113.6W 40 KT 45 MPH 36H 12/0000Z 24.3N 114.7W 35 KT 40 MPH...POST-TROPICAL 48H 12/1200Z 23.4N 115.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 60H 13/0000Z 22.4N 117.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 13/1200Z 21.6N 118.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 14/1200Z 20.7N 121.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 15/1200Z 20.0N 123.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Reinhart
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