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Post-Tropical Cyclone HERMINE Forecast Discussion Number 29
2016-09-04 16:48:46| National Hurricane Center (Atlantic)
Issued at 1100 AM AST SUN SEP 04 2016 000 WTNT44 KNHC 041448 TCDAT4 POST-TROPICAL CYCLONE HERMINE DISCUSSION NUMBER 29 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 1100 AM AST SUN SEP 04 2016 Hermine continues to have the structure of a post-tropical cyclone, with practically all of the deep convection well removed to the north-northeast of the center. An Air Force reconnaissance aircraft measured peak surface winds near 60 kt, and that value is used for the advisory intensity. Since the cyclone is over warm waters and the vertical shear may decrease somewhat during the next couple of days, some partial transition back to a tropical cyclone is possible. However, this is not explicitly indicated in the official forecast. In any event, the intensity of the system should be at or near hurricane force over the next 48 hours or so. Based on center fixes from the aircraft, the initial motion is 060/9 kt. A mid-tropospheric short wave trough will approach Hermine within the next day or so, and the global models forecast this vorticity maximum to merge with Hermine. This interaction is expected to cause the post-tropical cyclone to move northeastward, then northward, and then north-northwestward during the next 36 hours or so. Since the center has already moved a little to the east of the previous track, the official forecast has been adjusted eastward. Later in the forecast period, the system should move east-northeastward, and away from the northeastern United States. The official track forecast is somewhat to the west of the latest multi-model consensus. The slow motion and large wind field associated with Hermine will result in a long duration of hazardous conditions along much of the mid-Atlantic coast extending into southern New England through the holiday weekend and into midweek. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 37.2N 69.6W 60 KT 70 MPH 12H 05/0000Z 37.6N 69.4W 60 KT 70 MPH...POST-TROPICAL 24H 05/1200Z 38.3N 69.8W 60 KT 70 MPH...POST-TROPICAL 36H 06/0000Z 38.7N 70.0W 65 KT 75 MPH...POST-TROPICAL 48H 06/1200Z 39.0N 70.0W 65 KT 75 MPH...POST-TROPICAL 72H 07/1200Z 40.0N 68.0W 60 KT 70 MPH...POST-TROPICAL 96H 08/1200Z 41.0N 66.0W 55 KT 65 MPH...POST-TROPICAL 120H 09/1200Z 42.0N 60.5W 50 KT 60 MPH...POST-TROPICAL $$ Forecaster Pasch
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Post-Tropical Cyclone HERMINE Forecast Discussion Number 28
2016-09-04 10:59:44| National Hurricane Center (Atlantic)
Issued at 500 AM EDT SUN SEP 04 2016 000 WTNT44 KNHC 040859 TCDAT4 POST-TROPICAL CYCLONE HERMINE DISCUSSION NUMBER 28 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 500 AM EDT SUN SEP 04 2016 The overall structure of Hermine has changed little during the past 6 hours. A ring of shallow convection has developed within 60-100 n mi northwest through northeast of the center, possibly due to that portion of the circulation passing over the Gulf Stream, where water temperatures are 29-30C. An earlier ASCAT-B pass indicated that winds had decreased to 50-55 kt, and recent data from an Air Force Reserve reconnaissance aircraft confirms that Hermine has peak winds of 55 kt. The initial motion estimate is 065/10 kt. Hermine is expected to move slowly northward and perhaps erratically during the next 36 hours as the post-tropical cyclone begins to interact with an approaching strong mid-/upper-level shortwave trough that is gradually becoming more negatively tilted based on water vapor imagery. By 36-48 hours, Hermine is expected to become vertically stacked beneath a cut-off low, which could result in the cyclone briefly stalling south of southern New England before lifting out to the northeast by 72 hours. The models are in fairly good agreement on this developing track scenario through about 36 hours, but then diverge significantly after that with the UKMET model turning Hermine farther west closer to the New Jersey coast while the ECMWF lifts out Hermine more quickly. The GFS solution lies between these two extremes, and the new forecast track closely follows that model. However, there remains low confidence in any particular model. Little change in strength is likely today. However, by late tonight and on Monday, the models indicate that at least 6 deg C of cooling in the mid-/upper-levels will occur when Hermine's low-level circulation moves underneath the cut-off low. The combination of the much cooler air aloft over SSTs of at least 27-28C should generate strong instability and some inner-core convection, possibly resulting in a Hermine making the transition to a subtropical cyclone and strengthening back to hurricane force. The guidance is in good agreement that the system should slowly weaken after 48 hours when the system will be moving over much cooler water north of the Gulf Stream. The intensity forecast closely follows a blend of the GFS-ECMWF model solutions. KEY MESSAGES: 1. The slow motion and large wind field associated with Hermine will result in a long duration of hazardous conditions along much of the mid-Atlantic coast extending into southern New England through the holiday weekend and into midweek. 2. Small changes in the meandering track of Hermine could result in large differences in the impacts along the mid-Atlantic coast during the next several days. In addition, there could be multiple occurrences of tropical storm conditions in some locations within the warning area during this time. 3. Although Hermine has become a post-tropical cyclone, NHC will continue to issue its full suite of advisory and warning products as long as the system remains a significant threat to land areas. 4. P-surge, the model that drives the Potential Storm Surge Flooding Graphic, is designed for a wind field typical of a tropical cyclone. The wind field of Hermine is very poorly represented by the P-surge model and as a result, Flooding Graphics prior to today's 11 am EDT advisory understated the inundation risk from the Carolinas northward. The NWS is using the GFS ensemble system instead of P-surge for ongoing issuances of the Potential Storm Surge Flooding Graphic to provide a more realistic depiction of the threat. 5. The Prototype Storm Surge Watch/Warning Graphic accounts for the current wind structure of Hermine, and therefore accurately identifies those areas at risk for life-threatening storm surge. This graphic will also continue to be produced for Hermine. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 36.8N 70.8W 55 KT 65 MPH 12H 04/1800Z 37.2N 70.3W 55 KT 65 MPH...POST-TROPICAL 24H 05/0600Z 37.7N 70.6W 60 KT 70 MPH...POST-TROPICAL 36H 05/1800Z 38.0N 71.0W 65 KT 75 MPH...POST-TROPICAL 48H 06/0600Z 38.5N 70.8W 65 KT 75 MPH...POST-TROPICAL 72H 07/0600Z 39.2N 70.0W 60 KT 70 MPH...POST-TROPICAL 96H 08/0600Z 40.3N 68.0W 55 KT 65 MPH...POST-TROPICAL 120H 09/0600Z 41.5N 63.5W 50 KT 60 MPH...POST-TROPICAL $$ Forecaster Stewart
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Post-Tropical Cyclone HERMINE Forecast Discussion Number 27
2016-09-04 04:54:14| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT SAT SEP 03 2016 000 WTNT44 KNHC 040254 TCDAT4 POST-TROPICAL CYCLONE HERMINE DISCUSSION NUMBER 27 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 1100 PM EDT SAT SEP 03 2016 Hermine has changed little in structure since the last advisory, with most of the deep convection situated well northeast of the center and dry, subsiding air wrapping around the southern semicircle. Earlier data from an Air Force Reserve Hurricane Hunter aircraft showed that the central pressure had risen to 998 mb, and that 55-60 kt surface winds were present about 70 n mi northwest of the center. Based on this, the initial intensity remains 60 kt. Hermine continues to move east-northeastward with the initial motion of 075/11. During the next 72 hours, a mid- to upper-level trough currently moving through the northeastern United States will move close to, and then over the top of, the post-tropical cyclone. During this evolution, Hermine is expected to move slowly northward and then northwestward as it makes at least a partial cyclonic loop. While the track guidance is in fair agreement for the first 48-72 hours, there remains significant spread later in the period on how fast the cyclone will move out to sea after it merges with the trough. The UKMET is very slow to move the system out, while the ECMWF is much faster. The GFS is between these extremes, and the current run shows a little faster motion than the previous run. The new forecast track is similar to the previous forecast through 72 hours, and then is somewhat faster in moving the system to the east-northeast. Overall, there remains low confidence in any particular model solution, and it should be noted that the GFS and UKMET both bring the center closer to land than the official forecast. Little change in strength is likely tonight. On Sunday and Monday, the interaction with the upper-level trough is expected to provide more favorable conditions for strengthening while the system is over sea surface temperatures of 28C or warmer, and the dynamical models all show some deepening during this period. Based on this, the intensity forecast calls for Hermine to become a hurricane-force low. The guidance is in good agreement that the system should slowly weaken after 48 hours, and this is indicated in the forecast as well. KEY MESSAGES: 1. The slow motion and large wind field associated with Hermine will result in a long duration of hazardous conditions along much of the mid-Atlantic coast extending into southern New England through the holiday weekend and into midweek. 2. Small changes in the meandering track of Hermine could result in large differences in the impacts along the mid-Atlantic coast during the next several days. In addition, there could be multiple occurrences of tropical storm conditions in some locations within the warning area during this time. 3. Although Hermine has become a post-tropical cyclone, NHC will continue to issue its full suite of advisory and warning products as long as the system remains a significant threat to land areas. 4. P-surge, the model that drives the Potential Storm Surge Flooding Graphic, is designed for a wind field typical of a tropical cyclone. The wind field of Hermine is very poorly represented by the P-surge model and as a result, Flooding Graphics prior to today's 11 am EDT advisory understated the inundation risk from the Carolinas northward. The NWS is using the GFS ensemble system instead of P-surge for ongoing issuances of the Potential Storm Surge Flooding Graphic to provide a more realistic depiction of the threat. 5. The Prototype Storm Surge Watch/Warning Graphic accounts for the current wind structure of Hermine, and therefore accurately identifies those areas at risk for life-threatening storm surge. This graphic will also continue to be produced for Hermine. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 36.5N 72.1W 60 KT 70 MPH...POST-TROPICAL 12H 04/1200Z 37.1N 71.2W 60 KT 70 MPH...POST-TROPICAL 24H 05/0000Z 37.6N 71.2W 65 KT 75 MPH...POST-TROPICAL 36H 05/1200Z 37.9N 71.5W 65 KT 75 MPH...POST-TROPICAL 48H 06/0000Z 38.3N 71.8W 65 KT 75 MPH...POST-TROPICAL 72H 07/0000Z 39.0N 71.5W 60 KT 70 MPH...POST-TROPICAL 96H 08/0000Z 40.0N 70.0W 55 KT 65 MPH...POST-TROPICAL 120H 09/0000Z 41.0N 66.5W 50 KT 60 MPH...POST-TROPICAL $$ Forecaster Beven
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Post-Tropical Cyclone HERMINE Forecast Discussion Number 26
2016-09-03 22:57:11| National Hurricane Center (Atlantic)
Issued at 500 PM EDT SAT SEP 03 2016 000 WTNT44 KNHC 032057 TCDAT4 POST-TROPICAL CYCLONE HERMINE DISCUSSION NUMBER 26 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 500 PM EDT SAT SEP 03 2016 Hermine has the look of an extratropical cyclone this afternoon, with most of the deep convection situated well northeast of the center and dry, subsiding air wrapping around the southern semicircle. This descending air resulted in a band of very strong winds over portions of the Outer Banks of North Carolina today, and those winds along with SFMR data from the aircraft support an initial intensity of 60 kt for this advisory. Hermine has an expansive wind field, with 34-kt winds extending about 200 miles from the center. Hermine is still expected to interact with a shortwave trough in the next couple of days over warm SSTs, which should result in some intensification, although the global models are a little less bullish this cycle. The NHC forecast continues to show Hermine at or near hurricane intensity for the next 72 hours, with slow weakening expected thereafter. After moving due eastward earlier today, the initial motion is now back toward the east-northeast at around 10 kt. Hermine should turn northward and slow to a crawl as it merges with the upper-level trough, and the NHC track shows only 2-3 kt of forward speed from 24 through 96 hours. The spread in the track model guidance has increased this cycle, with the UKMET and GFS now showing more of a westward motion and are slower to begin moving Hermine northeastward. The ECMWF has trended eastward and is much faster, taking Hermine south of Cape Cod in about 4 days, while the GFS and UKMET are still centered offshore of New Jersey at that time. Given the spread, and the possibility of looping motions during the interaction with the upper trough, confidence in the details of the track forecast remains quite low. The new NHC track tries to maintain some continuity with the last one, but lies to the right of the previous one in the first 12-24 hours due to the more easterly motion of Hermine today. The NHC forecast is close to the multi-model consensus through 72 hours. After that time, the NHC track is faster than the new consensus but slower than the previous forecast, reflecting the increasing spread at those times and low confidence in any particular solution. KEY MESSAGES: 1. The slow motion and large wind field associated with Hermine will result in a long duration of hazardous conditions along much of the mid-Atlantic coast extending into southern New England through the holiday weekend and into midweek. 2. Small changes in the meandering track of Hermine could result in large differences in the impacts along the mid-Atlantic coast during the next several days. In addition, there could be multiple occurrences of tropical storm conditions in some locations within the warning area during this time. 3. Although Hermine has become a post-tropical cyclone, NHC will continue to issue its full suite of advisory and warning products as long as the system remains a significant threat to land areas. 4. P-surge, the model that drives the Potential Storm Surge Flooding Graphic, is designed for a wind field typical of a tropical cyclone. The wind field of Hermine is very poorly represented by the P-surge model and as a result, Flooding Graphics prior to today's 11 am EDT advisory understated the inundation risk from the Carolinas northward. The NWS is using the GFS ensemble system instead of P-surge for ongoing issuances of the Potential Storm Surge Flooding Graphic to provide a more realistic depiction of the threat. 5. The Prototype Storm Surge Watch/Warning Graphic accounts for the current wind structure of Hermine, and therefore accurately identifies those areas at risk for life-threatening storm surge. This graphic will also continue to be produced for Hermine. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 36.2N 73.3W 60 KT 70 MPH...POST-TROPICAL 12H 04/0600Z 36.8N 72.0W 60 KT 70 MPH...POST-TROPICAL 24H 04/1800Z 37.2N 71.3W 65 KT 75 MPH...POST-TROPICAL 36H 05/0600Z 37.7N 71.6W 65 KT 75 MPH...POST-TROPICAL 48H 05/1800Z 38.0N 72.0W 65 KT 75 MPH...POST-TROPICAL 72H 06/1800Z 38.8N 71.9W 60 KT 70 MPH...POST-TROPICAL 96H 07/1800Z 40.0N 71.0W 55 KT 65 MPH...POST-TROPICAL 120H 08/1800Z 41.0N 68.5W 50 KT 60 MPH...POST-TROPICAL $$ Forecaster Brennan
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Post-Tropical Cyclone HERMINE Forecast Discussion Number 25
2016-09-03 16:57:08| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT SAT SEP 03 2016 000 WTNT44 KNHC 031457 TCDAT4 POST-TROPICAL CYCLONE HERMINE DISCUSSION NUMBER 25 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 1100 AM EDT SAT SEP 03 2016 Satellite imagery indicates that Hermine has become a post-tropical cyclone, with the coldest convective tops now located more than 200 n mi northeast of the exposed center. Despite this change in structure, surface data from the Outer Banks indicate that some strong winds persist near the center, and the initial intensity is set to 55 kt for this advisory. During the next 48 to 72 hours, Hermine will interact with a strong mid-latitude shortwave trough and all of the global models show the system re-intensifying during that time and a redevelopment of a stronger inner core, albeit one situated underneath an upper-level low. Regardless of its final structure, Hermine is expected to remain a dangerous cyclone through the 5 day period. The initial motion estimate is a somewhat uncertain 060/14. Hermine should continue moving northeastward in deep-layer southwesterly flow through 24 hours and then meander generally northward from 36 to 72 hours while the cyclone deepens beneath the upper-level low. Late in the period, the guidance is in generally good agreement showing a steadier motion toward the northeast, although there is significant spread. The new NHC forecast is generally close to the previous one and is near a consensus of the GFS and ECMWF through 3 days, and then favors the guidance that is a bit faster and farther north at days 4 and 5. KEY MESSAGES: 1. The slow motion and large wind field associated with Hermine will result in a long duration of hazardous conditions along much of the mid-Atlantic coast extending into southern New England through the holiday weekend. 2. Although Hermine has become a post-tropical cyclone, NHC will continue to issue its full suite of advisory and warning products as long as the system remains a significant threat to land areas. 3. P-surge, the model that drives the Potential Storm Surge Flooding Graphic, is designed for a wind field typical of a tropical cyclone. The wind field of Hermine is very poorly represented by the P-surge model and as a result, recent Flooding Graphics have understated the inundation risk from the Carolinas northward. NHC will be discontinuing runs of the P-surge model for Hermine with this advisory. The NWS is attempting to substitute the GFS ensemble system for P-surge for the next issuance of the Potential Storm Surge Flooding Graphic, to provide a more realistic depiction of the threat. If this effort is unsuccessful, issuance of the Potential Storm Surge Flooding Graphic for Hermine will also be discontinued. 4. The Prototype Storm Surge Watch/Warning Graphic does account for the current wind structure of Hermine, and therefore accurately identifies those areas at risk for life-threatening storm surge. This graphic will continue to be produced for Hermine. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 36.1N 75.2W 55 KT 65 MPH...POST-TROPICAL 12H 04/0000Z 37.1N 73.0W 60 KT 70 MPH...POST-TROPICAL 24H 04/1200Z 37.9N 71.6W 60 KT 70 MPH...POST-TROPICAL 36H 05/0000Z 38.4N 71.6W 65 KT 75 MPH...POST-TROPICAL 48H 05/1200Z 38.7N 71.9W 65 KT 75 MPH...POST-TROPICAL 72H 06/1200Z 39.5N 71.5W 65 KT 75 MPH...POST-TROPICAL 96H 07/1200Z 40.4N 70.2W 60 KT 70 MPH...POST-TROPICAL 120H 08/1200Z 41.0N 67.5W 50 KT 60 MPH...POST-TROPICAL $$ Forecaster Brennan
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