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Post-Tropical Cyclone SEYMOUR Forecast Discussion Number 21
2016-10-28 10:35:23| National Hurricane Center (East Pacific)
Issued at 200 AM PDT FRI OCT 28 2016 000 WTPZ45 KNHC 280835 TCDEP5 POST-TROPICAL CYCLONE SEYMOUR DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL EP202016 200 AM PDT FRI OCT 28 2016 The cyclone has lacked organized deep convection within 60-100 n mi of its center for over 12 hours, and no longer qualifies as a tropical cyclone. Since Seymour has become a post-tropical remnant low, advisories are being discontinued. Subjective Dvorak classifications from TAFB and SAB along with scatterometer data indicated an intensity of near 35 kt at 0600 UTC. Assuming some additional spindown of the cyclone since then, the advisory intensity is set at 30 kt. The low will be moving through an extremely hostile environment of southwesterly shear of 40-45 kt and SSTs cooler than 23 deg C during the next couple of days. These environmental factors should cause the remnant low to dissipate in a couple of days. This is also shown by the global model predictions. The low has turned toward a slightly east of northward heading, and the initial motion is about 010/7 kt. A north-northeastward motion, ahead of an approaching frontal system, is expected over the next day or so. The official track forecast is adjusted a little to the left of the previous one, toward the latest model consensus. For additional information on the remnant low please see High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFEPI, WMO header FZPN02 KWBC, and on the web at http://www.opc.ncep.noaa.gov/shtml/NFDHSFEPI.shtml. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 22.4N 122.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 12H 28/1800Z 23.3N 122.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 29/0600Z 24.5N 121.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 29/1800Z 25.8N 121.2W 15 KT 15 MPH...POST-TROP/REMNT LOW 48H 30/0600Z 27.5N 121.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 72H 31/0600Z...DISSIPATED $$ Forecaster Pasch
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Tropical Storm SEYMOUR Forecast Discussion Number 20
2016-10-28 04:34:21| National Hurricane Center (East Pacific)
Issued at 800 PM PDT THU OCT 27 2016 000 WTPZ45 KNHC 280234 TCDEP5 TROPICAL STORM SEYMOUR DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL EP202016 800 PM PDT THU OCT 27 2016 A small area of deep convection has been ongoing more than 100 n mi north-northeast of Seymour's center during the past few hours, but it's not really enough to be considered organized. Dvorak Current Intensity numbers from TAFB and SAB decreased to 3.0/45 kt at 0000 UTC, and more recent ADT estimates are even lower. The advisory intensity is therefore set at 40 kt. Strong shear and colder waters ahead of Seymour should continue the fast weakening trend, and the cyclone is likely to be declared a remnant low in 12 hours or less due to a lack of organized deep convection. Based on global model fields, the remnant low is expected to dissipate just after 48 hours. Seymour has turned northward with an initial motion of 360/9 kt. As a shallow, convection-less low, Seymour is expected to turn northeastward ahead of a cold front during the next 24 hours and then back to the north-northeast by 48 hours. The new NHC track forecast is nearly identical to the previous advisory during the first 24 hours, but is then nudged westward at 36 and 48 hours in line with a general westward shift in the guidance at those times. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 22.0N 123.0W 40 KT 45 MPH 12H 28/1200Z 23.1N 122.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 29/0000Z 24.2N 121.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 29/1200Z 25.5N 121.1W 15 KT 15 MPH...POST-TROP/REMNT LOW 48H 30/0000Z 27.2N 120.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 72H 31/0000Z...DISSIPATED $$ Forecaster Berg
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Hurricane SEYMOUR Forecast Discussion Number 18
2016-10-27 16:33:16| National Hurricane Center (East Pacific)
Issued at 800 AM PDT THU OCT 27 2016 000 WTPZ45 KNHC 271433 TCDEP5 HURRICANE SEYMOUR DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL EP202016 800 AM PDT THU OCT 27 2016 Seymour is rapidly weakening due to a combination of southwesterly vertical wind shear and decreasing sea surface temperatures, with recent microwave imagery showing the low-level center becoming exposed to the south of the remaining deep convection. The initial intensity is lowered to 70 kt based on a blend of satellite intensity estimates and continuity from the last advisory, and it is possible this could be generous. Rapid weakening should continue, and Seymour is forecast to weaken to a tropical storm later today, become a remnant low in 36 hours or less, and dissipate completely between 48-72 hours. The initial motion is 335/10. Seymour is forecast to turn northward later today, and then north-northeastward tonight or on Friday ahead of a large deep-layer trough located well offshore of the west coast of the United States. The track guidance remains tightly clustered and the new forecast track, which lies near the center of the guidance envelope, is an update of the previous track. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 20.2N 122.7W 70 KT 80 MPH 12H 28/0000Z 21.5N 122.7W 55 KT 65 MPH 24H 28/1200Z 23.0N 122.0W 35 KT 40 MPH 36H 29/0000Z 24.3N 120.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 29/1200Z 25.6N 120.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 30/1200Z...DISSIPATED $$ Forecaster Beven
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Hurricane SEYMOUR Forecast Discussion Number 17
2016-10-27 10:37:45| National Hurricane Center (East Pacific)
Issued at 200 AM PDT THU OCT 27 2016 000 WTPZ45 KNHC 270837 TCDEP5 HURRICANE SEYMOUR DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL EP202016 200 AM PDT THU OCT 27 2016 Cool waters and strong southwesterly shear are causing Seymour to rapidly weaken this morning. The cloud pattern of the tropical cyclone is becoming increasingly asymmetric, with the center located near the southwestern edge of the main convective mass. As a result of the degradation of the cloud pattern, subjective and objective Dvorak T- and CI-numbers are quickly decreasing, and the initial intensity has been reduced to 80 kt for this advisory. Seymour will be moving over SSTs below 25 degrees Celsius and into an area of vertical shear greater than 30 kt within 12 hours. These hostile conditions will cause a rapid decrease in wind speed during the next 24 to 36 hours, and Seymour is predicted to weaken to a tropical storm this afternoon, and become a post-tropical remnant low by Friday afternoon. The hurricane has turned north-northwestward, and is moving 335 degrees at 10 kt. Seymour is forecast to turn northward today, and then northeastward on Friday ahead of a large deep-layer trough located well offshore of the west coast of the United States. The track guidance remains tightly clustered but has trended slightly faster this cycle. The updated NHC track forecast has been adjusted accordingly and lies near the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 19.5N 122.1W 80 KT 90 MPH 12H 27/1800Z 21.0N 122.6W 60 KT 70 MPH 24H 28/0600Z 22.6N 122.2W 40 KT 45 MPH 36H 28/1800Z 24.0N 121.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 29/0600Z 25.3N 120.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 30/0600Z...DISSIPATED $$ Forecaster Brown
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Hurricane SEYMOUR Forecast Discussion Number 16
2016-10-27 04:35:16| National Hurricane Center (East Pacific)
Issued at 800 PM PDT WED OCT 26 2016 000 WTPZ45 KNHC 270235 TCDEP5 HURRICANE SEYMOUR DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL EP202016 800 PM PDT WED OCT 26 2016 Seymour is weakening rapidly. Although a small eye was still apparent in microwave data a few hours ago, this feature is no longer evident in the latest geostationary satellite images. In addition, the convective pattern has become asymmetric due to increasing southwesterly shear. The initial wind speed is lowered to 95 kt based on Dvorak final T- and CI-numbers from TAFB, SAB, and CIMSS at the University of Wisconsin. The hurricane is moving across the 26 deg C isotherm and it is expected to move over even colder waters during the next couple of days. These unfavorable oceanic conditions combined with drier air and a significant increase in wind shear should cause Seymour to continue to rapidly weaken. The NHC intensity forecast shows a very fast weakening trend, predicting Seymour to fall below hurricane strength on Thursday and degenerate to a remnant low on Friday. This forecast lies near the middle of the intensity guidance envelope. The hurricane has made the expected turn to the northwest, and is now moving 320 degrees at 12 kt. A large deep-layer trough located several hundred miles offshore of the U.S. west coast is expected to move eastward, causing Seymour to slow down and turn northward and then northeastward during the next couple of days. The track models are in good agreement, and the NHC track forecast lies near the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 18.7N 121.7W 95 KT 110 MPH 12H 27/1200Z 20.1N 122.5W 75 KT 85 MPH 24H 28/0000Z 21.8N 122.7W 55 KT 65 MPH 36H 28/1200Z 23.2N 122.0W 35 KT 40 MPH...POST-TROPICAL 48H 29/0000Z 24.3N 121.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 30/0000Z...DISSIPATED $$ Forecaster Cangialosi
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