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Tropical Depression Fifteen-E Forecast Discussion Number 3
2021-09-08 10:49:33| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Wed Sep 08 2021 000 WTPZ45 KNHC 080849 TCDEP5 Tropical Depression Fifteen-E Discussion Number 3 NWS National Hurricane Center Miami FL EP152021 300 AM MDT Wed Sep 08 2021 The circulation of the depression has continued to become better defined, and there has been a substantial increase in deep convection within bands to the north and northeast of the center. However, the inner core remains slightly displaced from this activity, and a combination of subjective and objective intensity estimates supports maintaining the cyclone as a 30-kt depression for this advisory. The system has either been meandering or its center re-formed yesterday, and the long-term motion is a drift toward the north-northwest (335 degrees) at about 3 kt. This motion is likely due to the depression being caught within weak steering currents between a mid-level low west of the Baja California peninsula and troughing extending across Mexico to the Gulf of Mexico. A strong mid-tropospheric high over the western United States should gradually cause the system to move faster toward the northwest during the next 2 to 3 days, bringing it very close to Baja California Sur in about 48 hours. Of the track models, the GFS and COAMPS-TC models are the solutions which bring the cyclone's center closest to Baja California Sur, while the ECMWF and UKMET models have the farther-offshore tracks. The new NHC track forecast splits the difference among these solutions and is a little east of the previous forecast during the first 36 hours to account for recent short-term motions. After 36 hours, it falls more or less in line with the previous prediction and is very close to the consensus aids, HWRF, and HMON. There are counteracting factors at play regarding the depression's future intensity. Although deep-layer shear is forecast to be low, the GFS suggests that moderate to strong mid-level shear could develop below the outflow level during the next 24-48 hours. Sea surface temperatures will be plenty warm for strengthening during the next 48 hours, yet upper-level divergence is not expected to be ideal. Since the system's circulation appears to be improving, steady strengthening is forecast during the first 48 hours, and the depression could become a short-lived hurricane while it passes the Baja California peninsula. This forecast is near the upper end of the guidance envelope, close to the GFS, HWRF, COAMPS-TC, and HCCA solutions. The cyclone will be moving over colder waters in 2-3 days, which should cause quick weakening and a degeneration to remnant low status by day 4. Key Messages: 1. Tropical Depression Fifteen-E is expected to strengthen to a tropical storm later today, and it could become a short-lived hurricane while it passes just to the southwest of southern portions of Baja California Sur Thursday and Friday. A Tropical Storm Watch is in effect for southern portions of Baja California Sur, and interests there should continue to monitor the progress of the depression. 2. Heavy rains associated with Tropical Depression Fifteen-E are possible across southern portions of Baja California Sur Thursday through Friday. This will pose a threat of flash flooding and mudslides. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 18.5N 107.1W 30 KT 35 MPH 12H 08/1800Z 19.1N 107.6W 40 KT 45 MPH 24H 09/0600Z 20.0N 108.4W 50 KT 60 MPH 36H 09/1800Z 21.1N 109.6W 60 KT 70 MPH 48H 10/0600Z 22.3N 111.2W 65 KT 75 MPH 60H 10/1800Z 23.3N 112.8W 55 KT 65 MPH 72H 11/0600Z 23.9N 114.5W 45 KT 50 MPH 96H 12/0600Z 24.1N 117.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 13/0600Z 23.6N 119.6W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg
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