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Tropical Storm IAN Forecast Discussion Number 16
2016-09-16 10:38:13| National Hurricane Center (Atlantic)
Issued at 500 AM AST FRI SEP 16 2016 000 WTNT45 KNHC 160837 TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 500 AM AST FRI SEP 16 2016 Cloud tops have warmed near the center of Ian overnight, but the cloud pattern in geostationary imagery still resembles that of a tropical cyclone. A small mid-level eye and a banding convective structure are also seen in a 0417 UTC AMSR-2 overpass from GCOM-W1. The initial intensity is set to 50 kt based on the latest ST3.0 classification from TAFB and the fast forward speed of the cyclone, which now exceeds 40 kt. Ian should become extratropical within 12 hours and then be absorbed by another front near or northeast of Iceland in about 48 hours, as indicated by the latest ECMWF and UKMET model solutions. The AMSR-2 pass mentioned above and a 0544 UTC SSM/I pass were helpful in locating the low-level center of Ian, and the initial motion estimate is a somewhat uncertain 040/42. The cyclone should continue moving quickly northeastward ahead of a large upper-level trough until it is absorbed. The new NHC track forecast is based on a blend of the tightly clustered global model guidance. The track, intensity, and wind radii forecasts are based largely on guidance from the Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 45.2N 40.8W 50 KT 60 MPH 12H 16/1800Z 50.1N 34.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 24H 17/0600Z 57.2N 25.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 17/1800Z 61.8N 18.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 18/0600Z...ABSORBED $$ Forecaster Brennan
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Tropical Storm KARL Forecast Discussion Number 8
2016-09-16 10:34:05| National Hurricane Center (Atlantic)
Issued at 500 AM AST FRI SEP 16 2016 000 WTNT42 KNHC 160833 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 500 AM AST FRI SEP 16 2016 Water vapor satellite imagery indicates that Karl is moving directly toward the base of a mid-/upper-level trough while being affected by at least 20 kt of westerly shear. A recent SSMIS microwave pass showed that the deep convection remains displaced to the northeast of the center. Since the structure of the cyclone has not changed since the last advisory, the initial intensity is held at 40 kt. The SSMIS data indicated that the center has moved a little north of previous position estimates, and the initial motion is now 280/11 kt. Karl may gain a little more latitude during the next 12-24 hours, but after that time a strong subtropical ridge is expected to force the cyclone to move south of due west or possibly west- southwestward between 36-48 hours. Once it reaches the western portion of the ridge and intensifies, Karl is likely to again gain some latitude, turning west-northwestward by days 4 and 5. The track models all agree on this scenario and keep Karl well to the east and northeast of the Leeward Islands during the five-day forecast period. Mainly because of the adjustment in the initial position, the new NHC track forecast is a little north of the previous forecast, and it lies closest to an average of the GFS and ECMWF solutions. Strong to moderate vertical shear is expected to persist for the next 24-36 hours, and little to no change in strength is anticipated during that time. Even after 36 hours, Karl will be moving through a dry environment over the central tropical Atlantic, but lower shear and warming sea surface temperatures could allow for at least gradual strengthening. The intensity models have trended a little bit higher at the end of the forecast period, and the new NHC forecast shows Karl potentially reaching hurricane intensity by day 5. This forecast is very close to the SHIPS and LGEM models. The initial 12-ft sea radii have been expanded considerably on this advisory based on recent altimeter wave height data. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 18.3N 33.4W 40 KT 45 MPH 12H 16/1800Z 18.7N 35.3W 40 KT 45 MPH 24H 17/0600Z 18.7N 38.0W 40 KT 45 MPH 36H 17/1800Z 18.3N 40.7W 40 KT 45 MPH 48H 18/0600Z 17.7N 43.3W 45 KT 50 MPH 72H 19/0600Z 17.6N 48.1W 50 KT 60 MPH 96H 20/0600Z 19.0N 53.0W 55 KT 65 MPH 120H 21/0600Z 21.5N 57.5W 65 KT 75 MPH $$ Forecaster Berg
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Tropical Storm IAN Forecast Discussion Number 15
2016-09-16 05:06:13| National Hurricane Center (Atlantic)
Issued at 1100 PM AST THU SEP 15 2016 000 WTNT45 KNHC 160305 TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 1100 PM AST THU SEP 15 2016 Ian has continued to accelerate northeastward within deep-layer southwesterly flow ahead of an approaching cold front and strong shortwave trough, and this general motion is expected for the next 2 days until the system becomes absorbed by a larger extratropical low. The new track forecast is essentially just an update of the previous advisory track and remains near the center of the tightly clustered NHC model guidance, close to the GFS and ECMWF consensus. The initial intensity remains at 45 kt based a 16/0034Z ASCAT-B overpass that contained few 43-kt wind vectors southeast of the well-defined low-level center. Ian is forecast to merge with a baroclinic zone and undergo extratropical transition during the next 12-36 hours, and in the process it is expected to strengthen to at least storm-force before it is absorbed by another extratropical low. The new intensity forecast is the same as the previous advisory based on the global models and guidance from the Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 42.9N 44.9W 45 KT 50 MPH 12H 16/1200Z 46.9N 39.5W 55 KT 65 MPH...POST-TROPICAL 24H 17/0000Z 53.3N 31.4W 60 KT 70 MPH...POST-TROP/EXTRATROP 36H 17/1200Z 58.9N 23.4W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 18/0000Z 63.3N 15.6W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 19/0000Z...ABSORBED $$ Forecaster Stewart
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Tropical Storm KARL Forecast Discussion Number 7
2016-09-16 04:56:34| National Hurricane Center (Atlantic)
Issued at 1100 PM AST THU SEP 15 2016 000 WTNT42 KNHC 160256 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 PM AST THU SEP 15 2016 During the past six hours, a significant increase in the amount and the organization of the deep convection has occurred near and over the well-defined low-level circulation center. The southwestern edge of the cold cloud canopy, characterized by tops as cold as -89C, has continued to expand southwestward over the center despite southwesterly vertical wind shear of 20-25 kt. The initial intensity has been increased to 40 kt based on a constrained Dvorak satellite estimate of 35 kt form TAFB, but with a data T-number of T3.0/45 kt using a shear pattern. A 15/2247Z partial ASCAT-B pass indicated several 35-36 kt surface wind vectors in the northeastern quadrant more than 60 nmi from the center. Based on continued improvement in the satellite presentation since the ASCAT pass, the initial intensity is set at 40 kt, making Karl the eleventh named storm of the season. Karl is moving westward or 275/11 kt. The cyclone is expected to move westward and then west-southwestward around a strengthening Atlantic subtropical ridge for the next 48-72 hours. After that time, the ridge is forecast to weaken some, allowing Karl to turn back toward the west and then west-northwest by day 5. The new NHC forecast is essentially on top of the previous advisory track, and lies close to the multi-model consensus TVCX and the Florida State Superensemble model. Karl is expected to remain in a moderate to strong vertical wind shear environment for the next 36 hours or so, which should inhibit significant intensification. After that time, however, the shear is forecast to decrease to around 5 kt for the remainder of the 120-h period. That would normally result in more robust strengthening while the cyclone is moving over 28-29C SSTs. However, Karl will also be moving through a very dry mid-level moisture regime during that time, so the intensification trend is forecast to be much slower than the climatological rate of 20 kt per day, and lies close to the SHIPS intensity forecast. The large 34-kt wind radius in the northeastern quadrant is based on the aforementioned ASCAT wind data. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 17.9N 32.5W 40 KT 45 MPH 12H 16/1200Z 18.0N 34.5W 40 KT 45 MPH 24H 17/0000Z 18.0N 37.1W 40 KT 45 MPH 36H 17/1200Z 17.8N 39.7W 40 KT 45 MPH 48H 18/0000Z 17.5N 42.4W 45 KT 50 MPH 72H 19/0000Z 17.1N 47.8W 50 KT 60 MPH 96H 20/0000Z 17.8N 52.7W 55 KT 65 MPH 120H 21/0000Z 19.0N 57.0W 60 KT 70 MPH $$ Forecaster Stewart
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Tropical Storm ORLENE Forecast Discussion Number 21
2016-09-16 04:40:35| National Hurricane Center (East Pacific)
Issued at 800 PM PDT THU SEP 15 2016 000 WTPZ41 KNHC 160240 TCDEP1 TROPICAL STORM ORLENE DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL EP162016 800 PM PDT THU SEP 15 2016 Several microwave images have arrived since the previous advisory, revealing that the low-level center of Orlene is displaced to the east of a small area of persistent deep convection. Dvorak data-T numbers from TAFB, SAB, and the UW-CIMSS ADT vary greatly, mainly due to the sensitivity of the Dvorak technique to the location of the low-level center. The initial intensity has been conservatively lowered by 10 knots to 55 kt based on a blend of the Dvorak estimates and an 1823 UTC ASCAT pass. The ASCAT pass only showed a maximum of about 45 kt, so this may still be a little high. Orlene continues to move into a very dry and thermodynamically stable environment, highlighted by a field of stratocumulus clouds that wrap around the western half of the tropical storm. All of the intensity guidance continues to indicate that this hostile environment will cause steady weakening. The intensity forecast has been lowered from the previous advisory, but is a little higher than the latest intensity consensus out of respect to the GFS which shows more gradual weakening. The GFS and HWRF suggest that the cyclone will lose all deep convection and become post-tropical within 96 hours, which is reflected in the official forecast. Almost no change has been made to the track forecast, aside from a slight eastward adjustment of the initial position. The global models remain in good agreement that the mid-level ridge located to the north of Orlene will steer the tropical storm westward over the next three days. After 72 hours, low-level easterlies should continue to steer the remnant low generally westward at a slightly slower forward speed. The track forecast remains very close to the multi-model ensemble mean. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 19.7N 123.8W 55 KT 65 MPH 12H 16/1200Z 19.5N 125.4W 50 KT 60 MPH 24H 17/0000Z 19.4N 127.7W 45 KT 50 MPH 36H 17/1200Z 19.3N 130.2W 40 KT 45 MPH 48H 18/0000Z 19.3N 132.8W 35 KT 40 MPH 72H 19/0000Z 19.3N 137.9W 30 KT 35 MPH 96H 20/0000Z 20.0N 142.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 21/0000Z 20.5N 145.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart/Zelinsky
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