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Tropical Storm Odette Forecast Discussion Number 1
2021-09-17 22:38:07| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Fri Sep 17 2021 000 WTNT45 KNHC 172037 TCDAT5 Tropical Storm Odette Discussion Number 1 NWS National Hurricane Center Miami FL AL152021 500 PM EDT Fri Sep 17 2021 The circulation associated with the area of low pressure off the U.S. Mid-Atlantic coast has become better defined today, with a new center having developed near a persistent cluster of deep convection. This system has some non-tropical characteristics, with a developing frontal boundary draped around the northern and western side of the circulation. Although the convection is being sheared off to the northeast of the center, the structure still resembles that of a tropical cyclone. An ASCAT-C pass from a few hours ago showed that maximum winds were 30-35 kt to the north of the center, thus advisories are being initiated on Tropical Storm Odette with 35-kt winds. With the re-formation of the center, the initial motion is uncertain but is estimated to be northeastward, or 045/13 kt. Odette is embedded between the subtropical ridge over the western Atlantic and a deep-layer trough over the U.S. Upper Midwest and central Canada. The approach of this trough should cause Odette to accelerate toward the northeast and then east-northeast during the next few days. After about day 3, there is significant divergence among the models. The GFS ejects the system northeastward and stalls it over the north Atlantic, south of Greenland. The ECMWF, UKMET, and Canadian models, however, stall the cyclone sooner and have it meandering south of Newfoundland on days 4 and 5. For now, the NHC track forecast shows Odette slowing down significantly on those days (less than 5 kt on day 5) and is a blend of the TVCA and HCCA consensus aids. Odette's transition to an extratropical cyclone is probably already underway. The storm is also centered over the Gulf Stream, where water temperatures are about 28 degrees Celsius, so in the short term it is likely that a combination of baroclinic and convective forcing will cause some intensification, despite deep-layer shear strengthening to near 30 kt. The global models suggest that Odette should become fully extratropical by 36 hours, and the intensity models indicate that the post-tropical low should peak in intensity in 48-60 hours. The low is then likely to occlude by day 3, a process which typically leads to gradual weakening, which is indicated in the official forecast. Odette is expected to affect portions of Newfoundland with strong winds and heavy rainfall Sunday and Sunday night as a post-tropical cyclone. Please refer to products from Environment Canada for additional information on potential impacts in Newfoundland. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 36.7N 71.8W 35 KT 40 MPH 12H 18/0600Z 38.3N 69.3W 40 KT 45 MPH 24H 18/1800Z 39.9N 65.9W 45 KT 50 MPH 36H 19/0600Z 41.6N 61.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 19/1800Z 43.6N 57.1W 55 KT 65 MPH...POST-TROP/EXTRATROP 60H 20/0600Z 45.0N 52.8W 55 KT 65 MPH...POST-TROP/EXTRATROP 72H 20/1800Z 46.0N 49.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 21/1800Z 47.0N 47.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 22/1800Z 47.5N 45.5W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg
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