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Post-Tropical Cyclone Odette Forecast Discussion Number 5
2021-09-18 22:34:37| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sat Sep 18 2021 221 WTNT45 KNHC 182034 TCDAT5 Post-Tropical Cyclone Odette Discussion Number 5 NWS National Hurricane Center Miami FL AL152021 500 PM AST Sat Sep 18 2021 Odette appears to have completed extratropical transition, perhaps a little earlier than the global models want to admit. The cyclone has developed a frontal structure similar to that of a bent back occlusion, with cold-air stratocumulus clouds advecting eastward to the south of the center behind the trailing cold front. In addition, the remaining deep convection is closer to the system's triple point than multiple-swirled center of circulation. The initial intensity is highly uncertain since all three ASCAT instruments completely missed the area where the strongest winds were likely to have been occurring, and it is held at 40 kt based on continuity. The post-tropical cyclone has turned to the east-northeast and is moving a little faster--now with a motion of 060/16 kt. Additional acceleration is expected during the next 24 hours while Odette is embedded in the mid-latitude westerlies. After 24 hours, Odette is expected to detach from the prevailing flow, which will cause the cyclone to slow down and meander southeast of Newfoundland by days 3 through 5. The track guidance has shifted slightly southward on this cycle, and the NHC forecast follows that trend and continues to hedge toward a consensus of the GFS and ECMWF models. Now that Odette is extratropical, global models indicate that baroclinic forcing should support strengthening and expanding of the gale-force wind field during the next couple of days. During this evolution, the strongest winds will also migrate to the northern and western side of the circulation. The frontal low is expected to occlude in about 3 days, coincident with the beginning of its meandering motion, and that occlusion process should cause a slow weakening of the winds through the end of the forecast period. One caveat is that some of the models have been hinting that the occluded low could redevelop deep convection near the center and transition to a tropical or subtropical cyclone, but there has not been enough consistency among the guidance to explicitly make that forecast. If the system's forecast track continues to shift southward toward warmer waters on days 3 through 5, that scenario could become a stronger possibility. Post-Tropical Cyclone Odette is forecast to affect portions of Newfoundland with strong winds and heavy rainfall Sunday and Monday. Please refer to products from the Canadian Hurricane Centre for additional information on potential impacts in Newfoundland. This is the last advisory issued by the National Hurricane Center on Odette. Additional information on this system can be found in High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and online at ocean.weather.gov/shtml/NFDHSFAT1.php FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 39.1N 65.1W 40 KT 45 MPH...POST-TROP/EXTRATROP 12H 19/0600Z 40.5N 62.1W 45 KT 50 MPH...POST-TROP/EXTRATROP 24H 19/1800Z 41.9N 58.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 20/0600Z 42.3N 54.4W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 20/1800Z 41.8N 51.3W 50 KT 60 MPH...POST-TROP/EXTRATROP 60H 21/0600Z 40.7N 48.9W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 21/1800Z 40.0N 47.2W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 22/1800Z 41.4N 47.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 23/1800Z 43.2N 48.8W 30 KT 35 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg
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Tropical Storm Odette Forecast Discussion Number 4
2021-09-18 16:49:32| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sat Sep 18 2021 000 WTNT45 KNHC 181449 TCDAT5 Tropical Storm Odette Discussion Number 4 NWS National Hurricane Center Miami FL AL152021 1100 AM AST Sat Sep 18 2021 Strong shear of about 30 kt from the west-southwest continues to push all of Odette's deep convection well to the east of the surface center. The center itself lacks some definition, with multiple low-level swirls rotating around a common point. Odette is well on its way through the extratropical transition process, with cold air advection noted on the west side of the circulation, and a band of overcast clouds on the north side of the developing warm front. We're awaiting some new ASCAT data, which should arrive soon, and for now the initial intensity remains 40 kt based on continuity. Odette is being picked up by the mid-latitude westerlies, and it is moving a little faster toward the northeast, or 055/15 kt. The cyclone should turn to the east-northeast and accelerate further later today, but then a significant slow down is expected on days 3 through 5 when Odette detaches from the mid-latitude flow and meanders to the southeast of Newfoundland. In contrast to yesterday, the global models are in much better agreement on this scenario, and the updated NHC track forecast has been hedged in the direction of the GFEX consensus aids, since the GFS and ECMWF global models should have a good handle on the behavior of an extratropical cyclone. The global models vary slightly on when extratropical transition will be complete, but the GFS- and ECMWF-based SHIPS diagnostics indicate that it should happen by this evening or tonight. Baroclinic forcing will likely be the main contributor to Odette's expected strengthening over the next few days, and the intensity models, including the GFS and ECMWF global models, have been consistent in showing the peak winds reaching about 55 kt in 36-48 hours. The post-tropical cyclone is expected to occlude and lose its upper-air support in about 48 hours, which should lead to gradual weakening through the end of the 5-day forecast period. Odette's wind field is expected to expand significantly during the next few days while the system becomes a strong post-tropical cyclone. The post-tropical cyclone is forecast to affect portions of Newfoundland with strong winds and heavy rainfall Sunday and Monday. Please refer to products from the Canadian Hurricane Centre for additional information on potential impacts in Newfoundland. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 38.5N 67.3W 40 KT 45 MPH 12H 19/0000Z 40.0N 64.2W 45 KT 50 MPH 24H 19/1200Z 41.8N 59.9W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 20/0000Z 42.7N 56.4W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 20/1200Z 42.8N 53.1W 55 KT 65 MPH...POST-TROP/EXTRATROP 60H 21/0000Z 42.2N 50.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 21/1200Z 41.5N 49.1W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 22/1200Z 41.3N 48.7W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 23/1200Z 42.7N 48.8W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg
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Tropical Storm Odette Forecast Discussion Number 3
2021-09-18 10:36:57| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sat Sep 18 2021 000 WTNT45 KNHC 180836 TCDAT5 Tropical Storm Odette Discussion Number 3 NWS National Hurricane Center Miami FL AL152021 500 AM AST Sat Sep 18 2021 Odette does not look very much like a tropical cyclone. All of the deep convection continues to be displaced well to the east of the poorly-defined center due to strong westerly shear. The circulation is elongated from southwest to northeast and contains multiple low-cloud swirls. The current intensity of the system is estimated to be near 40 kt based on earlier scatterometer observations, and these stronger winds are occurring in the convection over the eastern semicircle of the cyclone, well removed from the center. Since the center is not so easy to locate, the motion is rather uncertain. However the system appears to be accelerating and the initial motion estimate is roughly 050/13 kt. Odette is embedded within the flow on the south side of a mid-latitude shortwave trough. This steering pattern should carry the system northeastward to east-northeastward for the next couple of days. Afterwards, the trough is predicted by the global models to cut off to the south of eastern Newfoundland. As a result, Odette is likely to turn a little south of east and decelerate in 3-4 days. By the end of the forecast period, the cyclone is expected to begin moving northeastward on the east side of the cutoff low. The official track forecast is similar to the previous one but a little farther south around days 4 and 5. This is in good agreement with the latest corrected model consensus. The dynamical guidance indicates that the vertical shear over Odette will get even stronger over the next few days. As the system will soon begin to move over the cooler waters to the north of the Gulf Stream, its primary energy source should come from baroclinicity. In about 24 hours, the dynamical guidance shows significant thermal advection around the cyclone, signifying its extratropical transition. The global models show the post-tropical cyclone deepening through 48 hours and the official forecast calls for some strengthening up to that time. Later in the period, as the baroclinic energy source appears to wane, gradual weakening is expected. As Odette becomes fully extratropical and gains latitude this weekend and into Monday, the wind field is forecast to expand significantly. Odette is expected to affect portions of Newfoundland with strong winds and heavy rainfall Sunday and Monday as a strong post-tropical cyclone. Please refer to products from Environment Canada for additional information on potential impacts in Newfoundland. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 38.0N 69.3W 40 KT 45 MPH 12H 18/1800Z 39.2N 66.7W 45 KT 50 MPH 24H 19/0600Z 40.8N 62.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 19/1800Z 42.4N 58.4W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 20/0600Z 43.3N 54.4W 55 KT 65 MPH...POST-TROP/EXTRATROP 60H 20/1800Z 43.5N 51.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 72H 21/0600Z 43.0N 48.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 22/0600Z 42.5N 46.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 23/0600Z 43.0N 46.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch
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Tropical Storm Odette Forecast Discussion Number 2
2021-09-18 04:33:43| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Fri Sep 17 2021 000 WTNT45 KNHC 180233 TCDAT5 Tropical Storm Odette Discussion Number 2 NWS National Hurricane Center Miami FL AL152021 1100 PM EDT Fri Sep 17 2021 Satellite images indicate that west-southwesterly shear is taking a toll on Odette. Deep convection has been separating from the low-level circulation, and the closest area of thunderstorms is now more than 100 miles east of the center. The circulation is rather broad, but there is a clear center a couple of hundred miles off the U.S. Mid-Atlantic coast. The initial intensity is held at 35 kt for this advisory. A very recent ASCAT pass showed some stronger winds in the thunderstorms more than a couple of hundred miles east of the low-level center, but its not clear if those winds are reliable and representative of the storm's true intensity. Hopefully more scatterometer data with be available soon to better assess Odette's strength. Although it appears that Odette has been meandering lately, a 12-hour average yields a northeastward motion at about 9 kt. The storm is expected to move faster northeastward or east-northeastward off the northeast U.S. and Atlantic Canada coasts this weekend as it moves in the mid-latitude flow. After that time, the models show a significant slow down as the cyclone cuts off from the progressive flow to the south or southeast of Newfoundland. Although there is quite a bit of spread in the models from days 3-5, almost all of the guidance shows the storm stalling by the end of the forecast period. The new NHC track forecast is a little to the south of the previous one to come into better agreement with the latest models. This forecast still lies to the north of the consensus aids, however. Odette is already beginning the process of transitioning to an extratropical cyclone, and it will likely complete the transition by Saturday night when it is expected to be north of the Gulf Stream Current and merging with an approaching trough. The cyclone is likely to reach its peak intensity as an extratropical storm in 48-60 hours when the baroclinic dynamics are most favorable. Gradual weakening seems likely beyond that time. The NHC intensity forecast is the same as the previous one and in line with the majority of the guidance. As Odette becomes fully extratropical and gains latitude this weekend, the wind field is forecast to expand significantly. 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 18/0300Z 36.4N 71.2W 35 KT 40 MPH 12H 18/1200Z 37.8N 69.3W 40 KT 45 MPH 24H 19/0000Z 39.4N 65.7W 45 KT 50 MPH...POST-TROP/EXTRATROP 36H 19/1200Z 41.0N 61.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 20/0000Z 42.3N 57.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 60H 20/1200Z 43.4N 53.1W 55 KT 65 MPH...POST-TROP/EXTRATROP 72H 21/0000Z 43.8N 50.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 22/0000Z 44.3N 48.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 23/0000Z 44.8N 46.6W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi
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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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