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Hurricane Norman Forecast Discussion Number 26

2018-09-03 16:46:56| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Mon Sep 03 2018 016 WTPZ41 KNHC 031446 TCDEP1 Hurricane Norman Discussion Number 26 NWS National Hurricane Center Miami FL EP162018 800 AM PDT Mon Sep 03 2018 Satellite images indicate that Norman is weakening. The eye is no longer apparent on infrared imagery, and the cloud tops are warming throughout the central dense overcast. The initial wind speed is reduced to 95 kt, which is close to a blend of the Dvorak CI numbers from TAFB and SAB. Continued weakening is likely over the next several days due to a combination of marginal SSTs, light or moderate shear, and a dry mid-level environment. The new forecast is very similar to the previous one, except lower in the short term to account for the current intensity. Norman has turned westward and is still moving at about 17 kt. A fast westward motion is anticipated over the next few days while a large subtropical ridge holds firm over the central Pacific Ocean. However, a weakness in the ridge from 150W-155W should cause Norman to turn more northwestward after day 3. Model guidance is showing considerable spread at long range, with the UKMET and its ensemble closer to Hawaii, while almost all of the other guidance is much farther northeast. There continues to be a westward shift in the guidance, so the official forecast has been shifted westward at long range. It should be noted, however, that there isn't much support for the UKMET solution in the rest of the guidance, so it seems to be an outlier at this time. Hopefully the NOAA G-IV aircraft dropsonde data this afternoon will help resolve these model differences for the 0000 UTC cycle. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 19.3N 136.6W 95 KT 110 MPH 12H 04/0000Z 19.7N 139.2W 85 KT 100 MPH 24H 04/1200Z 20.0N 142.3W 75 KT 85 MPH 36H 05/0000Z 20.2N 144.8W 70 KT 80 MPH 48H 05/1200Z 20.3N 146.9W 70 KT 80 MPH 72H 06/1200Z 21.3N 150.1W 65 KT 75 MPH 96H 07/1200Z 24.0N 152.5W 60 KT 70 MPH 120H 08/1200Z 27.5N 154.5W 45 KT 50 MPH $$ Forecaster Blake

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Tropical Storm Florence Forecast Discussion Number 17

2018-09-03 16:43:24| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Mon Sep 03 2018 541 WTNT41 KNHC 031443 TCDAT1 Tropical Storm Florence Discussion Number 17 NWS National Hurricane Center Miami FL AL062018 1100 AM AST Mon Sep 03 2018 While Florence's structure improved overnight, the cloud tops have warmed and the deep convection has thinned during the past several hours. The 12Z satellite intensity estimates range from 55 to 65 kt, but given recent trends the initial intensity is set at the low end of that range at 55 kt, although this is quite uncertain given the recent fluctuations in the cloud pattern. UW-CIMSS satellite diagnostics indicate that around 20 kt of southwesterly shear is affecting Florence, while the SHIPS analysis based on the GFS fields shows only about 10 kt. SSTs warm from this point forward along the forecast track, but shear is expected to be steady or strengthen, and the mid-level relative humidity values decrease to around 50 percent during the next 48 to 72 hours. Given these mixed factors, the NHC intensity forecast shows some possibility for strengthening in the next 12 hours, followed by a slow decay through 72 hours. Some restrengthening is forecast late in the period as SSTs warm above 28C and the atmospheric moisture increases. The NHC forecast is close to or a bit above the latest IVCN consensus aid and about 5 kt above the previous NHC forecast through 96 hours. The initial motion estimate is 285/14. Florence will be steered generally west-northwestward for the next 72 hours by the Atlantic subtropical ridge, followed by a northwestward turn at days 4 and 5. While there is large spread in the guidance between the HWRF on the right and the UKMET on the left, the GFS, ECMWF, and their ensemble means are more tightly clustered near the middle of the guidance envelope. Since the overall track forecast reasoning has not changed, the new NHC forecast remains near the middle of the guidance. This forecast is a bit north of the previous NHC track given the initial position and lies a little south of the consensus aids to reflect less influence of the outlier HWRF model to the north. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 18.3N 38.7W 55 KT 65 MPH 12H 04/0000Z 18.6N 40.7W 60 KT 70 MPH 24H 04/1200Z 19.1N 43.0W 60 KT 70 MPH 36H 05/0000Z 19.9N 45.3W 55 KT 65 MPH 48H 05/1200Z 20.8N 47.6W 50 KT 60 MPH 72H 06/1200Z 23.0N 52.2W 45 KT 50 MPH 96H 07/1200Z 25.0N 55.0W 50 KT 60 MPH 120H 08/1200Z 27.0N 58.0W 55 KT 65 MPH $$ Forecaster Brennan

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Tropical Storm Olivia Forecast Discussion Number 11

2018-09-03 16:40:52| Tropical Depression LIDIA

Issued at 900 AM MDT Mon Sep 03 2018

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Tropical Storm Gordon Forecast Discussion Number 4

2018-09-03 14:36:27| National Hurricane Center (Atlantic)

Issued at 830 AM EDT Mon Sep 03 2018 678 WTNT42 KNHC 031236 TCDAT2 Tropical Storm Gordon Special Discussion Number 4 NWS National Hurricane Center Miami FL AL072018 830 AM EDT Mon Sep 03 2018 Surface observations from the Florida Keys and southeast Florida, along with Doppler velocity data from the Miami radar, indicate that the disturbance has developed a closed surface circulation and a well-defined center. Recent observations from a Weatherflow site at Carys Fort Reef and radar data support increasing the maximum winds to at least 40 kt. As a result of these data, the system has been upgraded to Tropical Storm Gordon, the seventh named system of the 2018 Atlantic hurricane season. An Air Force Reserve Unit reconnaissance aircraft is enroute to investigate Gordon. The initial motion estimate is 300/15 kt and the previous forecast track remains unchanged. The intensity forecast was adjusted upward in the first 24 to 36 hours to account for the initial increase in intensity. Some additional adjustments may be required after the reconnaissance aircraft completes its mission and provides more detailed information on the stricture and intensity of Gordon. Key Messages: 1. Gordon will bring heavy rainfall and tropical storm conditions to portions of South Florida and the Florida Keys today and a Tropical Storm Warning is in effect for these areas. 2. A Tropical Storm Warning is in effect for portions of the central Gulf Coast, and tropical storm conditions are expected in those areas beginning late Tuesday. Heavy rainfall from Gordon will affect portions of the central Gulf Coast over the next few days, including areas that have already received heavy rainfall from a different weather system. Interests in these areas should monitor products from their local National Weather Service office. FORECAST POSITIONS AND MAX WINDS INIT 03/1230Z 25.1N 80.7W 40 KT 45 MPH 12H 03/1800Z 25.7N 82.1W 45 KT 50 MPH 24H 04/0600Z 27.2N 84.8W 50 KT 60 MPH 36H 04/1800Z 28.8N 87.4W 50 KT 60 MPH 48H 05/0600Z 30.4N 89.7W 50 KT 60 MPH 72H 06/0600Z 33.0N 92.7W 30 KT 35 MPH...INLAND 96H 07/0600Z 34.0N 95.0W 25 KT 30 MPH...INLAND 120H 08/0600Z 35.5N 96.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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Potential Tropical Cyclone Seven Forecast Discussion Number 3

2018-09-03 11:05:23| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Mon Sep 03 2018 003 WTNT42 KNHC 030904 CCA TCDAT2 Potential Tropical Cyclone Seven Discussion Number 3...Corrected NWS National Hurricane Center Miami FL AL072018 500 AM EDT Mon Sep 03 2018 Corrected motion in second paragraph The system is gradually becoming better organized with some increased convective banding features. However, surface and radar data suggest that a well-defined center of circulation has not yet formed. The initial intensity is set at 25 kt in agreement with the latest Dvorak estimates from TAFB and SAB. An Air Force Reserve Unit Hurricane Hunter aircraft is scheduled to investigate the system later this morning, and should provide a better estimate of its intensity and structure. Global model predictions show a closed circulation forming within 12 to 24 hours, so the official forecast calls for tropical cyclone status later today. Although the system should move over the very warm waters of the eastern and north-central Gulf of Mexico during the next 36 hours, the model guidance is not very aggressive about intensification. This may be due to some moderate shear as indicated by the SHIPS model output. The official intensity forecast is similar to the previous one and at the upper end of the numerical guidance suite. The disturbance appears to have picked up some forward speed, and is now moving at around 300/14 kt. A west-northwestward to northwestward motion is likely, along the southwestern periphery of a mid-level anticyclone, until landfall along the northern Gulf coast. The official track forecast is close to the dynamical model consensus and is just slightly to the right of and faster than the previous one. Given the proximity of the 36-hour forecast point to the coast, it is time to change the Tropical Storm Watch to a Warning. 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 today, and interests in those areas should monitor the progress of this system. 2. A Tropical Storm Warning has been issued for portions of the central Gulf Coast, and tropical storm conditions are expected in those areas beginning late Tuesday. Heavy rainfall from this system will affect portions of the central Gulf Coast over the next few days, including areas that have already received 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 cyclones is generally larger than that for tropical cyclones, especially beyond 48-72 hours. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 24.5N 80.2W 25 KT 30 MPH...POTENTIAL TROP CYCLONE 12H 03/1800Z 25.7N 82.1W 30 KT 35 MPH 24H 04/0600Z 27.2N 84.8W 35 KT 40 MPH 36H 04/1800Z 28.8N 87.4W 40 KT 45 MPH 48H 05/0600Z 30.4N 89.7W 50 KT 60 MPH 72H 06/0600Z 33.0N 92.7W 30 KT 35 MPH...INLAND 96H 07/0600Z 34.0N 95.0W 25 KT 30 MPH...INLAND 120H 08/0600Z 35.5N 96.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Pasch

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