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Tropical Storm Florence Forecast Discussion Number 15

2018-09-03 04:35:40| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sun Sep 02 2018 741 WTNT41 KNHC 030235 TCDAT1 Tropical Storm Florence Discussion Number 15 NWS National Hurricane Center Miami FL AL062018 1100 PM AST Sun Sep 02 2018 Florence has generally changed little during the past several hours. The cloud pattern consists of a central dense overcast feature with the low-level center estimated to be closer to the southern side of the convection. All of the satellite intensity estimates have held steady and support maintaining the wind speed at 45 kt. Although Florence is located in an environment of relatively low wind shear, the SSTs beneath the cyclone are cool, around 26 deg C. The tropical storm is expected to move over gradually warmer waters beginning in about 24 hours, but it will also be moving into an environment of higher shear. These mixed signals suggest that Florence will likely change little in intensity or weaken slightly during the next few days. By the end of the forecast period, however, the shear is expected to lessen and by then Florence should be over much warmer waters. Therefore, strengthening seems likely in the 4 to 5 day time period. The NHC intensity forecast is a little lower than the previous one to come into better agreement with the latest guidance. Florence is moving west-northwestward at 15 kt steered by a mid-level ridge to its northeast. Although the track models all show a west-northwestward to northwestward motion during the next several days, the north-south spread becomes fairly large by the end of the forecast period. This spread appears to be primarily associated with differences on how strong or vertically coherent each model predicts Florence to be. Since the NHC forecast shows the storm changing little in strength for the next few days, this track prediction lies near the middle of the guidance envelope close to the various consensus models. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 17.9N 35.9W 45 KT 50 MPH 12H 03/1200Z 18.3N 38.1W 45 KT 50 MPH 24H 04/0000Z 18.7N 40.6W 45 KT 50 MPH 36H 04/1200Z 19.2N 43.0W 45 KT 50 MPH 48H 05/0000Z 19.8N 45.2W 45 KT 50 MPH 72H 06/0000Z 21.5N 49.6W 40 KT 45 MPH 96H 07/0000Z 23.6N 53.8W 40 KT 45 MPH 120H 08/0000Z 25.5N 56.7W 50 KT 60 MPH $$ Forecaster Cangialosi

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Hurricane Norman Forecast Discussion Number 24

2018-09-03 04:32:59| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Sun Sep 02 2018 256 WTPZ41 KNHC 030232 TCDEP1 Hurricane Norman Discussion Number 24 NWS National Hurricane Center Miami FL EP162018 800 PM PDT Sun Sep 02 2018 Satellite images indicate that Norman is maintaining its strength this evening. The eye of the hurricane remains distinct and a ring of cold cloud tops surrounds that feature. However, the cloud tops have been warming a little during the past few hours. A blend of the latest satellite intensity estimates supports holding the initial wind speed at 115 kt. Norman is currently located over marginally warm 27 deg C SSTs and it will be moving over slightly cooler waters during the next several days. In addition, the global models show the hurricane moving into an increasingly drier air mass and show a significant increase in shear in 4 to 5 days. All of these conditions suggest that Norman should steadily weaken, and the NHC forecast follows the trend in the model guidance. This forecast is in best agreement with the consensus models HCCA and IVCN. Norman continues to move fairly quickly to the west-northwest, with the latest initial motion estimate the same as before, 285/17. This motion is expected to continue for the next day or so while Norman remains steered by a strong subtropical ridge to its north-northeast. After that time, a decrease in forward speed and then a gradual turn to the northwest are predicted as Norman moves near the edge of the ridge and approaches a significant weakness caused by a large-scale trough. The models agree on this overall scenario, but they differ on the details of where and when Norman makes the northwestward turn. The NHC track forecast lies near the middle of the guidance envelope and is near the typically most skillful aids, the consensus models. Based on this forecast, Norman is expected to cross into the central Pacific basin in 24 to 36 hours. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 18.6N 132.7W 115 KT 130 MPH 12H 03/1200Z 19.2N 135.3W 105 KT 120 MPH 24H 04/0000Z 19.9N 138.6W 95 KT 110 MPH 36H 04/1200Z 20.4N 141.6W 80 KT 90 MPH 48H 05/0000Z 20.7N 144.0W 75 KT 85 MPH 72H 06/0000Z 21.5N 148.0W 70 KT 80 MPH 96H 07/0000Z 23.4N 150.9W 60 KT 70 MPH 120H 08/0000Z 26.2N 153.2W 50 KT 60 MPH $$ Forecaster Cangialosi

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Potential Tropical Cyclone Seven Forecast Discussion Number 1

2018-09-02 22:46:46| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Sun Sep 02 2018 713 WTNT42 KNHC 022046 TCDAT2 Potential Tropical Cyclone Seven Discussion Number 1 NWS National Hurricane Center Miami FL AL072018 500 PM EDT Sun Sep 02 2018 The area of disturbed weather associated with a tropical wave that the NHC has been tracking for the past few days has become better organized today. Strong winds previously associated with an upper- level trough just west of the system have decreased significantly during the day, and the upper-level flow across the disturbance has become more anticyclonic. Earlier scatterometer wind data indicated that the system does not yet have a closed surface circulation. However, the same data indicate that winds of 25-28 kt exist outside of thunderstorm activity, with some higher gusts likely present. The initial intensity is being set at a conservative 25 kt for this advisory. The initial motion estimate is an uncertain 300/13 kt. The global models are in excellent agreement that the strong subtropical ridge to the north of the disturbance will remain entrenched across the southeastern U.S. and mid-Atlantic states throughout the forecast period. This flow pattern should keep the system moving in a west- northwestward to northwestward motion until landfall occurs along the central Gulf coast in 60-72 hours. The model tracks are tightly packed, so the NHC official forecast track essentially lies down the middle of the guidance envelope. On the forecast track, the system is expected to move across the Florida Keys Monday afternoon, and reach the central Gulf Coast by Tuesday night or Wednesday morning. The aforementioned upper-level anticyclonic has been steadily increasing during the day today, with weak cirrus outflow now occurring in all quadrants. The disturbance is forecast to move across the very warm waters of the Gulfstream late tonight and early Monday morning where local diabatic heating should enhance deep convection near the mid-level circulation, causing the vortex column to build downward to the surface. Once a closed surface circulation develops, the combination of low to modest vertical shear and SSTs of at least 30C along the track should allow for at least slow but steady strengthening. Although the official intensity forecast shows weakening at 72 hours, this is due to the system expected to be inland at that time. Conditions will favorable for continued strengthening after the 48-h period until landfall occurs, and a peak intensity of around 55 kt around 60 hours is possible. The SHIPS and LGEM models were the only intensity guidance available for this package, and the official forecast is just a little below an average of those models. The HWRF and HMON models will be forthcoming for the next advisory package, so some adjustments to this first intensity forecast may be required as more guidance becomes available. Key Messages: 1. Potential Tropical Cyclone Seven will bring heavy rainfall and gusty winds to portions of the Bahamas, South Florida, and the Florida Keys tonight and Monday, and interests in those areas should monitor the progress of this system. 2. A Tropical Storm Watch has been issued for portions of the central Gulf Coast, and tropical storm conditions are possible in those areas Tuesday night and Wednesday. Heavy rainfall from this system will affect portions of the central Gulf Coast later this week, including areas that are currently receiving heavy rainfall from a different weather system. Interests in these areas should monitor products from their local National Weather Service office. 3. Users should be aware that forecast uncertainty for potential tropical cylones is generally larger than that for tropical cyclones, especially beyond 48-72 hours. FORECAST POSITIONS AND MAX WINDS INIT 02/2100Z 22.7N 77.3W 25 KT 30 MPH...POTENTIAL TROP CYCLONE 12H 03/0600Z 23.7N 79.3W 30 KT 35 MPH...TROPICAL DEPRESSION 24H 03/1800Z 25.1N 81.9W 35 KT 40 MPH 36H 04/0600Z 26.6N 84.5W 40 KT 45 MPH 48H 04/1800Z 28.0N 87.1W 50 KT 60 MPH 72H 05/1800Z 30.6N 91.6W 35 KT 40 MPH...INLAND 96H 06/1800Z 33.0N 94.0W 25 KT 30 MPH...INLAND 120H 07/1800Z 34.0N 95.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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Tropical Storm Olivia Forecast Discussion Number 8

2018-09-02 22:39:48| Tropical Depression LIDIA

Issued at 300 PM MDT Sun Sep 02 2018

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Tropical Storm Florence Forecast Discussion Number 14

2018-09-02 22:34:19| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sun Sep 02 2018 671 WTNT41 KNHC 022034 TCDAT1 Tropical Storm Florence Discussion Number 14 NWS National Hurricane Center Miami FL AL062018 500 PM AST Sun Sep 02 2018 Florence's cloud pattern is characterized by a low-level center partially displaced to the west of the coldest cloud tops, which have expanded in coverage recently. A blend of the latest satellite classifications supports maintaining an intensity of 45 kt for this advisory package. Little change in strength is expected for much of the forecast period, as Florence will be moving through an environment characterized by moderate shear and marginal SSTs for the next 3 days. By the end of the forecast period, the SSTs begin to warm up, which should result in some restrengthening. The new NHC intensity forecast is similar to the previous one and is closest to the SHIPS model forecast. The initial motion estimate is 285/15. Florence will be steered west-northwestward or westward for the next several days by the Atlantic subtropical ridge. There is a fair amount of north-south spread in the guidance, with the GFS, GEFS ensemble mean and HWRF on the right side of the envelope and the ECMWF, ECMWF mean and UKMET on the left. This spread is likely due to large differences in the vertical structure of the cyclone, with the ECMWF and UKMET having a much weaker vortex at 500 mb compared to the GFS in 3-4 days. Given the difficulty in forecasting these types of structural changes, the NHC forecast lies in the middle of the guidance envelope and is close to the multi-model consensus aids through the forecast period. This forecast is largely an update of the previous NHC prediction. FORECAST POSITIONS AND MAX WINDS INIT 02/2100Z 17.4N 34.6W 45 KT 50 MPH 12H 03/0600Z 17.7N 36.9W 45 KT 50 MPH 24H 03/1800Z 18.2N 39.6W 45 KT 50 MPH 36H 04/0600Z 18.6N 41.9W 45 KT 50 MPH 48H 04/1800Z 19.3N 44.0W 45 KT 50 MPH 72H 05/1800Z 21.1N 48.3W 45 KT 50 MPH 96H 06/1800Z 23.0N 52.0W 45 KT 50 MPH 120H 07/1800Z 25.5N 56.0W 55 KT 65 MPH $$ Forecaster Brennan

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