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Tropical Storm Florence Forecast Discussion Number 9
2018-09-01 16:44:38| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sat Sep 01 2018 056 WTNT41 KNHC 011444 TCDAT1 Tropical Storm Florence Discussion Number 9 NWS National Hurricane Center Miami FL AL062018 1100 AM AST Sat Sep 01 2018 Satellite images indicate that Florence's cloud pattern has improved in organization with the low-level center embedded within the convection, and a cyclonically curved band surrounding the system. A blend of subjective and objective Dvorak numbers from TAFB, SAB, and the UW-CIMMS yield an initial intensity of 40 kt. My predecessor wrote a very clear explanation of the reasoning of his track and intensity forecasts, and I do not think I can improve on it. The environment continues to be mixed with favorable and unfavorable conditions for Florence to strengthen. Currently, the shear is low and favors strengthening, but the ocean along the cyclone's forecast path is cooler. The latter condition should inhibit significant intensification. After 3 days, the opposite is anticipated -- the ocean will be warmer, but the shear will likely be high. Only at the very long range could both factors become favorable. The best option at this time is to show only a gradual strengthening at the rate indicated by the intensity consensus aids. Florence is still moving toward the west-northwest or 295 degrees at 12 kt. No change in track is anticipated during the next 3 days while Florence is located to the south of the subtropical ridge. After that time, Florence will reach a break in the ridge causing the cyclone to turn toward the northwest with a decrease in forward speed. The confidence in the forecast is high during the next 3 days when the track guidance envelope is tightly packed. Thereafter, the confidence is not so high since the envelope widens and becomes bounded by the easternmost HWRF and the westernmost ECMWF models. Since the guidance envelope shifted a little bit westward, the NHC forecast was also adjusted slightly in that direction, primarily during the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 14.8N 27.8W 40 KT 45 MPH 12H 02/0000Z 15.3N 29.7W 45 KT 50 MPH 24H 02/1200Z 16.1N 32.4W 50 KT 60 MPH 36H 03/0000Z 16.5N 35.0W 50 KT 60 MPH 48H 03/1200Z 17.0N 37.5W 55 KT 65 MPH 72H 04/1200Z 19.0N 42.5W 60 KT 70 MPH 96H 05/1200Z 21.0N 46.5W 60 KT 70 MPH 120H 06/1200Z 23.5N 50.0W 55 KT 65 MPH $$ Forecaster Avila
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Tropical Storm Florence Forecast Discussion Number 8
2018-09-01 10:56:36| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sat Sep 01 2018 081 WTNT41 KNHC 010856 TCDAT1 Tropical Storm Florence Discussion Number 8 NWS National Hurricane Center Miami FL AL062018 500 AM AST Sat Sep 01 2018 A recent SSMIS microwave pass has revealed that the cyclone has become much better organized with more pronounced convective banding. Satellite intensity estimates are wide ranging, spanning from T1.5/25 kt from SAB to T3.4/53 kt from the UW-CIMSS ADT. Since the numbers overall have increased, and the structure has improved, the initial intensity is raised to 35 kt, in closest agreement to the TAFB estimate, but this could be conservative. This makes the depression Tropical Storm Florence, the sixth named storm of the season. Florence is moving west-northwestward, or 285/12 kt, and should maintain this motion for the next 48 hours while traveling along the southern periphery of the subtropical ridge. After 48 hours, the storm is expected to reach a break in the ridge, causing it to slow down and turn northwestward by day 5. The biggest change noted among the track models on this cycle was a westward shift in the overall guidance envelope. The European model, in particular, swung significantly to the left, showing a weaker Florence not feeling the break in the ridge quite as much. I'd like to see this trend continue before making a significant change to the forecast, so for now the updated NHC track prediction is only nudged westward. That said, the models appear to be trending away from a definitive recurvature scenario. The environment is mixed with positives and negatives for Florence's strengthening. For the first 3 days, vertical shear over Florence should be quite low, but the cyclone will also be moving through a less-than-ideal thermodynamic environment with marginal sea surface temperatures and decreasing mid-level moisture. After 3 days, the thermodynamic environment should begin to improve, but then the shear is forecast to strengthen. These conflicting signals point to only gradual strengthening, and the suite of intensity models aren't too far off from one another, nor from the previous NHC forecast. For that reason, no significant changes were made in this forecast package. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 14.5N 26.7W 35 KT 40 MPH 12H 01/1800Z 15.0N 28.7W 40 KT 45 MPH 24H 02/0600Z 15.7N 31.2W 45 KT 50 MPH 36H 02/1800Z 16.4N 33.7W 50 KT 60 MPH 48H 03/0600Z 17.1N 36.3W 55 KT 65 MPH 72H 04/0600Z 18.7N 41.4W 60 KT 70 MPH 96H 05/0600Z 21.0N 45.5W 60 KT 70 MPH 120H 06/0600Z 23.5N 48.5W 55 KT 65 MPH $$ Forecaster Berg
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Hurricane Norman Forecast Discussion Number 17
2018-09-01 10:34:06| National Hurricane Center (East Pacific)
Issued at 200 AM PDT Sat Sep 01 2018 873 WTPZ41 KNHC 010834 TCDEP1 Hurricane Norman Discussion Number 17 NWS National Hurricane Center Miami FL EP162018 200 AM PDT Sat Sep 01 2018 Norman continues to weaken due to the effects of moderate northeasterly shear of about 20 kt, as analyzed in SHIPS diagnostics. The hurricane has taken on a traditional IR shear pattern structure, with a tight gradient of brightness temperatures observed up-shear of the estimated center position. Satellite intensity estimates have continued to drop and no longer support keeping Norman at major hurricane strength. The initial intensity has been lowered to 95 kt, just above the latest SATCON estimate, but this still could be generous. The shear affecting Norman is expected to continue for at least the next 24 h. Some of the dynamical models hint that the shear could relax between 24-48 h, which would likely bring an end to Norman's weakening trend. While it is not explicitly reflected in the intensity forecast, a decrease in shear could even allow the hurricane to briefly restrengthen. Recent microwave imagery indicates that the mid- to lower-level inner-core and eye of Norman are still intact. If this structure can survive the next 24 h of shear, reintensification would be more likely. By 72 h, the hurricane will reach drier, more stable air and moderate SSTs, and these factors will likely cause it to steadily weaken through the remainder of the forecast period. The cyclone appears to have finally turned westward, and the initial motion is 265/7 kt. No significant changes have been made to the track forecast. Norman is still expected to move westward to west-northwestward for the next several days, steered primarily by an extensive deep-layer ridge to the north. The models remain in good agreement on the track of Norman throughout the forecast period, and the official track forecast is near the middle of the guidance envelope and very close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 16.3N 123.0W 95 KT 110 MPH 12H 01/1800Z 16.3N 124.4W 85 KT 100 MPH 24H 02/0600Z 16.6N 126.8W 85 KT 100 MPH 36H 02/1800Z 17.3N 129.8W 85 KT 100 MPH 48H 03/0600Z 18.2N 132.9W 85 KT 100 MPH 72H 04/0600Z 19.9N 139.1W 70 KT 80 MPH 96H 05/0600Z 21.0N 143.5W 65 KT 75 MPH 120H 06/0600Z 21.5N 147.0W 60 KT 70 MPH $$ Forecaster Zelinsky
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Tropical Depression Seventeen-E Forecast Discussion Number 2
2018-09-01 10:32:36| Tropical Depression LIDIA
Issued at 300 AM MDT Sat Sep 01 2018
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Hurricane Norman Forecast Discussion Number 16
2018-09-01 04:51:06| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Fri Aug 31 2018 508 WTPZ41 KNHC 010251 TCDEP1 Hurricane Norman Discussion Number 16 NWS National Hurricane Center Miami FL EP162018 800 PM PDT Fri Aug 31 2018 Several recent microwave passes indicate that Norman continues to feel the effects of northeasterly shear, with the cyclone vertically titled and its upper-level core disrupted in the northern semicircle. Furthermore, the eye of the hurricane has disappeared on IR and visible imagery. Satellite intensity estimates from TAFB and SAB have also decreased since the previous advisory, and therefore, the initial intensity has been decreased to 105 kt, and this value could be a little generous. Model guidance continues to indicate moderate northeasterly shear over the cyclone for the next day or so, which should cause the gradual weakening to continue. Thereafter, the shear is forecast to lessen somewhat, but the cyclone is expected to begin entraining dry air from its surrounding environment. There may be some time between 24-48 hours when the lessening shear and warm SSTs could overcome the drier air in the environment to allow for either a steadying of intensity or perhaps even some slight re-strengthening. Beyond 48 hours, however, the environment is forecast to become even drier, which should induce another weakening trend. The NHC intensity forecast has been changed little through 24 h, but now shows a leveling off of the intensity from 24-48 h. Steady weakening is still anticipated beyond that time. The initial motion is estimated to be west-southwest, or 250/7 kt. Mid- to upper-level ridging that extends west-southwestward from the Baja California peninsula to just northwest of the cyclone should steer Norman west-southwestward for the next several hours. By Saturday morning, the ridge should begin to become oriented more east-to-west then southeast-to-northwest by Sunday. This will cause the system to be steered on a more westward then west-northwestward track with an increase in forward speed over the weekend and into early next week. The NHC track forecast has been shifted slightly left and is a little faster than the previous advisory. This forecast is generally between the previous NHC forecast and the consensus guidance track. Based on this forecast, Norman is expected to move into the central Pacific basin by Tuesday. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 16.3N 122.2W 105 KT 120 MPH 12H 01/1200Z 16.2N 123.6W 95 KT 110 MPH 24H 02/0000Z 16.4N 125.9W 90 KT 105 MPH 36H 02/1200Z 17.0N 128.7W 90 KT 105 MPH 48H 03/0000Z 17.7N 131.8W 90 KT 105 MPH 72H 04/0000Z 19.1N 138.0W 80 KT 90 MPH 96H 05/0000Z 20.3N 142.7W 70 KT 80 MPH 120H 06/0000Z 21.2N 146.3W 65 KT 75 MPH $$ Forecaster Cangialosi/Latto
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