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Hurricane Dorian Forecast Discussion Number 56
2019-09-07 10:39:54| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sat Sep 07 2019 460 WTNT45 KNHC 070839 TCDAT5 Hurricane Dorian Discussion Number 56 NWS National Hurricane Center Miami FL AL052019 500 AM AST Sat Sep 07 2019 Dorian is gradually becoming less organized. The cyclone is feeling some effects of southwesterly wind shear with most of its deep convection located to the north and east of the estimated center. The initial intensity is lowered a little to 75 kt, which is in good agreement with the latest Dvorak CI-numbers from TAFB and SAB. A pair of ASCAT passes from several hours ago indicate that the wind field has expanded significantly, and tropical-storm-force winds have been observed over far southeastern Massachusetts. Dorian is racing northeastward, with the latest initial motion estimated to be 050/22 kt. The hurricane is well embedded in the fast mid-latitude flow, and it should continue to move quickly northeastward toward Nova Scotia later today. After the cyclone passes Nova Scotia, it is forecast to move through Newfoundland and Labrador before turning east-northeastward over the far north Atlantic. The NHC track forecast is largely an update of the previous one and not far from the various consensus aids. Dorian is expected to gradually weaken due to even stronger southwesterly wind shear and much colder SSTs to the north of the Gulf Stream current. The combined influences of these cold waters and an approaching mid- to upper-level trough should cause Dorian to lose its tropical characteristics in about 24 hours. However, the post-tropical cyclone will likely still be producing hurricane-force winds as it moves through portions of eastern Canada. The global models are in good agreement that the post-tropical cyclone should slowly weaken and ultimately become absorbed by another extratropical low in 3 to 4 days. The NHC intensity forecast is in best agreement with the GFS and ECMWF models, which typically handle large extratropical lows better that than the intensity models that are made for tropical cyclones. Key Messages: 1. Regardless of whether it is a hurricane or a post-tropical cyclone, Dorian is expected to have a significant impact in portions of eastern Canada beginning later today. Dangerous storm surge impacts are likely in portions of the Gulf of St. Lawrence, southwestern Newfoundland and eastern Nova Scotia. Hurricane-force winds are also likely in Nova Scotia, Prince Edward Island and Newfoundland later today and tonight. Refer to information from the Canadian Hurricane Centre for more information on these hazards. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 39.7N 68.1W 75 KT 85 MPH 12H 07/1800Z 42.8N 64.9W 70 KT 80 MPH 24H 08/0600Z 46.9N 61.6W 65 KT 75 MPH...POST-TROP/EXTRATROP 36H 08/1800Z 50.0N 58.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 09/0600Z 52.5N 52.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 10/0600Z 57.5N 36.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 11/0600Z...DISSIPATED $$ Forecaster Cangialosi
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Tropical Storm Gabrielle Forecast Discussion Number 15
2019-09-07 10:37:20| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sat Sep 07 2019 000 WTNT43 KNHC 070837 TCDAT3 Tropical Storm Gabrielle Discussion Number 15 NWS National Hurricane Center Miami FL AL082019 500 AM AST Sat Sep 07 2019 Gabrielle's cloud pattern has temporarily degraded over the past several hours. With the vertical shear pattern shifting from the east, the shrinking, shapeless, convective mass is displaced to the west of the surface circulation. A blend of the Dvorak subjective satellite T-numbers yields a current intensity estimate of 35 kt, and a UW-CIMSS ADT estimate as well as an AMSU-A analysis come in at 39 kt. The initial intensity is generously above these data and is set at 45 kt out of respect for the earlier scatterometer wind analysis. Gabrielle has moved to the northeast of the upper cut-off low which has been producing a moderate to strong southerly shear environment over the past several days. The upper wind pattern in this quadrant of the upper low is more easterly, and although still quite strong, a little more diffluent. This slightly more favorable flow aloft, along with increasingly warmer sea surface temperatures in the region, should allow Gabrielle to gradually strengthen during the next 2 to 3 days. Toward the end of the forecast period, weakening is forecast to commence as the cyclone turns northeastward and quickly moves within deep-layer strong southwesterly flow associated with an approaching mid-latitude baroclinic frontal zone. Interaction with the frontal system as well as the cyclone traversing significantly decreasing oceanic temperatures (less than 20C), should induce a rather rapid extratropical transition around day 5. The NHC intensity forecast is an update of the previous one is above all of the guidance with the exception of the HWRF. The initial motion is estimated to be northwestward, or 310/15 kt. Azores high pressure to the northeast of Gabrielle is forecast to build over the north central Atlantic, causing the cyclone to turn west-northwestward later today. Afterward, southwesterly flow downstream from the aforementioned front should force Gabrielle to turn northward and northeastward on Sunday and Monday, respectively. A slight adjustment to the left of the previous forecast was made through the entire forecast in order to align more with the NOAA HFIP HCCA model. Some adjustments to the wind radii were made based on a 06 Sep 2320 UTC ASCAT-A/B ambiguity analysis. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 30.9N 42.1W 45 KT 50 MPH 12H 07/1800Z 31.9N 44.3W 50 KT 60 MPH 24H 08/0600Z 33.3N 46.6W 55 KT 65 MPH 36H 08/1800Z 35.4N 47.9W 60 KT 70 MPH 48H 09/0600Z 38.0N 47.3W 65 KT 75 MPH 72H 10/0600Z 43.6N 40.3W 75 KT 85 MPH 96H 11/0600Z 50.7N 26.7W 65 KT 75 MPH 120H 12/0600Z 59.4N 7.9W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Roberts
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Tropical Storm Juliette Forecast Discussion Number 25
2019-09-07 10:34:52| National Hurricane Center (East Pacific)
Issued at 1100 PM HST Fri Sep 06 2019 000 WTPZ41 KNHC 070834 TCDEP1 Tropical Storm Juliette Discussion Number 25 NWS National Hurricane Center Miami FL EP112019 1100 PM HST Fri Sep 06 2019 Juliette is rapidly declining and is well on its way to becoming post-tropical. Cloud tops have warmed dramatically over the past few hours, and satellite intensity estimates have decreased sharply in turn. ASCAT data that arrived shortly before 06Z revealed that Juliette is not as strong as previously estimated, with max winds of only 35-40 kt. Based on that new info, the intensity has been adjusted down to 40 kt. The main change in the NHC forecast is that it now shows Juliette becoming post-tropical in 24 hours. Given current trends, it could certainly happen much sooner than that. Otherwise, the overall reasoning behind the forecast is the same. Juliette is located over quite cold waters and will steadily spin down over the next several days. The tropical storm has turned westward and should continue heading west through the middle of next week, steered by low-level easterly trade winds. This track will take the soon-to-be remnant low over warmer waters by day 5, and some of the dynamical guidance suggests that Juliette could try to make a comeback at that time. However, extremely high wind shear should prevent any convection that does develop from becoming organized and regeneration is not expected. The NHC track and intensity forecasts remain very close to the various consensus aids throughout the 5-day period. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 23.8N 127.1W 40 KT 45 MPH 12H 07/1800Z 24.0N 128.8W 35 KT 40 MPH 24H 08/0600Z 24.0N 131.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 08/1800Z 24.0N 133.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 09/0600Z 23.9N 135.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 10/0600Z 23.7N 139.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 11/0600Z 23.5N 142.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 12/0600Z 24.0N 145.0W 25 KT 30 MPH...DISSIPATED $$ Forecaster Zelinsky
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Hurricane Dorian Forecast Discussion Number 55
2019-09-07 04:49:47| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Fri Sep 06 2019 000 WTNT45 KNHC 070249 TCDAT5 Hurricane Dorian Discussion Number 55 NWS National Hurricane Center Miami FL AL052019 1100 PM EDT Fri Sep 06 2019 During the past couple of hours Dorian's eye has become no longer apparent in conventional satellite imagery. Microwave data shows an eye-like feature just to the south of the convection, and also indicates that the hurricane is becoming asymmetric. The lack of symmetry is the first indication or hint that Dorian is slowly beginning to acquire some extratropical characteristics. The rain shield is now placed to the northwest of the center, and the wind field is expanding in the southern semicircle. Dvorak numbers are either steady or have decreased slightly, and consequently the initial intensity is kept at 80 kt in this advisory. The hurricane is rapidly reaching cooler waters and guidance shows an area of significantly strong shear along the forecast path of Dorian. Given these conditions, the NHC forecast calls for gradual weakening, but Dorian is still expected to make landfall in Nova Scotia with hurricane intensity late Saturday. Dorian is forecast to complete its transition to extratropical once it crosses Nova Scotia. The hurricane is racing northeastward or 045 degrees at 22 kt. Since Dorian is already embedded within a fast southwesterly flow ahead of a mid-latitude trough, the current northeast heading should continue until dissipation occurs in about 3 days, if not sooner. The track guidance is in remarkably good agreement, and the NHC forecast is in the middle of the guidance envelope, increasing the confidence in the track forecast. Key Messages: 1. Regardless of whether it is a hurricane or a post-tropical cyclone, Dorian is expected to have a significant impact in portions of eastern Canada. Dangerous storm surge impacts are likely in portions of the Gulf of St. Lawrence, southwestern Newfoundland and eastern Nova Scotia this weekend. Hurricane-force winds are also likely in Nova Scotia, Prince Edward Island and possibly Newfoundland Saturday and Sunday. Refer to information from the Canadian Hurricane Centre for more information on these hazards. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 38.3N 70.2W 80 KT 90 MPH 12H 07/1200Z 40.8N 66.9W 75 KT 85 MPH 24H 08/0000Z 45.0N 63.0W 70 KT 80 MPH...INLAND 36H 08/1200Z 49.0N 59.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 09/0000Z 52.0N 55.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 10/0000Z 56.0N 41.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 11/0000Z...DISSIPATED $$ Forecaster Avila
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Tropical Storm Gabrielle Forecast Discussion Number 14
2019-09-07 04:33:46| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Fri Sep 06 2019 000 WTNT43 KNHC 070233 TCDAT3 Tropical Storm Gabrielle Discussion Number 14 NWS National Hurricane Center Miami FL AL082019 1100 PM AST Fri Sep 06 2019 Deep convection has persisted mainly over the northern semicircle of Gabrielle since this afternoon, but has been trying to move a little closer to the low-level center. The subjective intensity estimate from TAFB suggests slight strengthening has occurred since the previous advisory, and a recent scatterometer pass measured a cluster of 45-kt winds. Assuming some slight undersampling in that area by the scatterometer, the initial advisory intensity has been increased to 50 kt. The shear that continues to impact Gabrielle is forecast to decrease through Saturday morning. Meanwhile, the cyclone will me moving over waters near 29 C. And, although some dry air will continue to surround the circulation, the cyclone should be able to gradually strengthen over the next few days due to the other favorable environmental conditions. After 72 hours, increasing southwesterly shear and cooler SSTs will cause the cyclone to weaken. An approaching mid-latitude trough, courtesy of Dorian, will help transition Gabrielle to an extratropical cyclone by the end of the forecast period. The only notable change to the intensity forecast from the previous advisory was to make Gabrielle a hurricane a little earlier, and the official advisory is very near the corrected consensus HCCA. Gabrielle has been moving to the northwest, or 320/16 kt. A turn to the west-northwest is expected to occur on Saturday as the subtropical ridge to the northeast of Gabrielle builds westward. The aforementioned mid-latitude trough will begin to turn Gabrielle to the north on Sunday night, then accelerate the cyclone to the northeast from Monday through the end of the forecast period. The official forecast is very similar to the previous one, and near the tightly clustered consensus guidance. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 29.3N 40.9W 50 KT 60 MPH 12H 07/1200Z 30.9N 42.9W 55 KT 65 MPH 24H 08/0000Z 32.1N 45.6W 60 KT 70 MPH 36H 08/1200Z 33.7N 47.5W 70 KT 80 MPH 48H 09/0000Z 35.7N 48.0W 75 KT 85 MPH 72H 10/0000Z 40.5N 44.0W 80 KT 90 MPH 96H 11/0000Z 47.0N 34.0W 70 KT 80 MPH 120H 12/0000Z 56.1N 16.5W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Latto
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