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Tropical Storm Harvey Forecast Discussion Number 6

2017-08-18 22:36:30| National Hurricane Center (Atlantic)

Issued at 500 PM AST Fri Aug 18 2017 000 WTNT44 KNHC 182036 TCDAT4 Tropical Storm Harvey Discussion Number 6 NWS National Hurricane Center Miami FL AL092017 500 PM AST Fri Aug 18 2017 Again, there has been little change in the structure of Harvey, with the low-level center near the eastern edge of a strong, but poorly organized, convective area. Earlier reports from an Air Force Reserve Hurricane Hunter aircraft included winds suggesting an increased intensity. However, due to uncertainties in how representative these measurements were, no appreciable change in the central pressure, and no improvement in the structure, the initial intensity is held at 35 kt. The initial motion is 275/18. A strong low- to mid-level ridge north of the cyclone should keep Harvey on this general motion for the next 3 days or so, with the system moving from the eastern to the western Caribbean Sea during this time. After 72 h, a west-northwestward motion with a decrease in forward speed is expected when Harvey passes near or over portions of Central America, the Yucatan Peninsula, and eastern Mexico. The new forecast track is a little faster then the previous track, but there were only minor changes in the direction. It should be noted that there is considerable uncertainty about how far north Harvey might get over the Bay of Campeche, with several of the large-scale models not bringing the center back over the water on the latest runs. The current shear should persist for about the next 48 h, and thus the intensity forecast continues the trend of slow strengthening during this time. However, the GFS and ECMWF again forecast Harvey to degenerate to an open wave during this time, and the rest of the intensity guidance has trended toward a weaker cyclone. This lowers the confidence in intensification. After 48 h, conditions appear more favorable for strengthening, with the main uncertainty being how much land Harvey will encounter. The intensity forecast will again call for a peak intensity of 60 kt in 72 h, followed by weakening due to land interaction. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 13.4N 62.9W 35 KT 40 MPH 12H 19/0600Z 13.6N 65.7W 35 KT 40 MPH 24H 19/1800Z 13.9N 69.3W 40 KT 45 MPH 36H 20/0600Z 14.2N 73.0W 40 KT 45 MPH 48H 20/1800Z 14.5N 76.7W 45 KT 50 MPH 72H 21/1800Z 15.5N 83.5W 60 KT 70 MPH 96H 22/1800Z 17.5N 88.5W 50 KT 60 MPH...INLAND 120H 23/1800Z 19.0N 92.0W 30 KT 35 MPH...OVER WATER $$ Forecaster Beven

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Tropical Storm Harvey Forecast Discussion Number 5

2017-08-18 16:50:53| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Fri Aug 18 2017 000 WTNT44 KNHC 181450 TCDAT4 Tropical Storm Harvey Discussion Number 5 NWS National Hurricane Center Miami FL AL092017 1100 AM AST Fri Aug 18 2017 The structure of Harvey has changed little during the past several hours, and overall the storm is poorly organized. The low-level center is near the eastern edge of the convective mass due to the affects of 15 kt of vertical wind shear. In addition, surface observations and Air Force Reserve Hurricane Hunter data suggest that the 850-mb center is located west or southwest of the surface center. Based on the aircraft and surface data, the central pressure is near 1005 mb and the initial intensity remains 35 kt. The initial motion is a quick 270/18. A strong low- to mid-level ridge north of the cyclone should keep Harvey on this general motion for the next 3-4 days, with the system moving from the eastern to the western Caribbean Sea during this time. Late in the forecast period, a more northerly motion is expected when Harvey passes near or over portions of Central America, the Yucatan Peninsula, and eastern Mexico. The new forecast track remains in the center of the guidance, and only minor changes were made to the previous track. The current shear should persist for the next 48 h or so, and thus the intensity forecast continues the trend of slow strengthening during this time. After that, conditions appear favorable for strengthening, with the main uncertainty being how much land Harvey will encounter. The ECMWF keeps the cyclone a little north of Nicaragua and Honduras and allows more room for development, while the GFS forecasts landfall in northeastern Nicaragua and thus has a weaker intensity. The new NHC forecast is close to the previous one in showing a peak intensity below hurricane strength, but the confidence in this portion of the forecast is low. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 13.1N 61.3W 35 KT 40 MPH 12H 19/0000Z 13.3N 63.8W 35 KT 40 MPH 24H 19/1200Z 13.6N 67.3W 40 KT 45 MPH 36H 20/0000Z 14.0N 71.1W 40 KT 45 MPH 48H 20/1200Z 14.3N 75.0W 50 KT 60 MPH 72H 21/1200Z 15.0N 82.0W 60 KT 70 MPH 96H 22/1200Z 16.5N 87.5W 55 KT 65 MPH 120H 23/1200Z 18.5N 91.0W 30 KT 35 MPH...INLAND $$ Forecaster Beven

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Tropical Depression Thirteen-E Forecast Discussion Number 1

2017-08-18 16:41:26| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Fri Aug 18 2017 000 WTPZ43 KNHC 181441 TCDEP3 Tropical Depression Thirteen-E Discussion Number 1 NWS National Hurricane Center Miami FL EP132017 800 AM PDT Fri Aug 18 2017 Deep convection associated with the disturbance located over the open eastern Pacific Ocean has become better organized early this morning, and a primary convective band now wraps around the western half of the circulation. Shortwave-IR and first-light visible imagery suggest that a complex, but closed surface circulation exists. NHC is therefore initiating advisories on Tropical Depression Thirteen-E. The initial intensity is set at 30 kt, in agreement with the max winds measured in an earlier ASCAT pass and the latest Dvorak classification from TAFB. Light easterly vertical wind shear has thus far limited convection to the western half of the circulation, but the GFS and ECMWF agree that the shear will lessen as the system moves farther west. Overall, the environment appears conducive for intensification for the next 3 days or so, and the NHC forecast indicates that the cyclone will become a hurricane by the end of this weekend. After that time, the cyclone will begin to weaken over much cooler waters. The NHC forecast is very close to the multi-model consensus, IVCN. Since the center has only recently formed, the initial motion estimate is a fairly uncertain 285/13 kt. There is fairly good agreement among the global models that the tropical cyclone will move generally westward to west-northwestward for the next 72 h along the southern boundary of a mid-level ridge that extends westward well into the eastern Pacific basin. A weakness in the ridge is forecast to develop in about 3 days that should cause the cyclone to slow and turn more toward the northwest and eventually toward the north-northwest. The official forecast is close to a blend of the GFS and ECMWF models. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 14.8N 116.5W 30 KT 35 MPH 12H 19/0000Z 15.4N 118.4W 35 KT 40 MPH 24H 19/1200Z 15.9N 121.0W 45 KT 50 MPH 36H 20/0000Z 16.6N 123.6W 55 KT 65 MPH 48H 20/1200Z 17.3N 126.1W 65 KT 75 MPH 72H 21/1200Z 19.1N 130.3W 75 KT 85 MPH 96H 22/1200Z 21.4N 132.4W 65 KT 75 MPH 120H 23/1200Z 23.6N 133.3W 45 KT 50 MPH $$ Forecaster Zelinsky

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Tropical Storm Harvey Forecast Discussion Number 3

2017-08-18 04:31:50| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Thu Aug 17 2017 000 WTNT44 KNHC 180231 TCDAT4 Tropical Storm Harvey Discussion Number 3 NWS National Hurricane Center Miami FL AL092017 1100 PM AST Thu Aug 17 2017 Since an Air Force Hurricane Hunter aircraft departed the storm a few hours ago, the cloud pattern of Harvey hasn't changed much. Dvorak intensity estimates from both TAFB and SAB are 30 kt, and based on the earlier aircraft measurements the current intensity is held at 35 kt. The storm is in a moderate easterly shear environment, which should allow only slow strengthening for the next couple of days. After that, the dynamical models indicate that a decrease in shear should occur. As noted earlier, however, the GFS and ECMWF global models do not show strengthening of Harvey and in fact practically dissipate it during the forecast period. This suggests something unfavorable in the environment besides shear ahead of the system, perhaps some drier air or subsidence. The official intensity forecast shows modest strengthening and is generally close to the model consensus which includes the statistical/dynamical guidance and the regional hurricane models (that do show some strengthening). The motion continues westward or 270/16. There is no change to the track forecast philosophy from the previous advisory package. Harvey should remain embedded in the flow on the south side of a strong mid-level ridge throughout most of the forecast period, which should steer the system on a continued westward track. Near the end of period, the guidance suggests a slightly more northward motion with some deceleration. The official forecast track is near the dynamical model consensus and very close to the previous NHC track. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 13.0N 57.4W 35 KT 40 MPH 12H 18/1200Z 13.2N 59.9W 35 KT 40 MPH 24H 19/0000Z 13.6N 63.3W 40 KT 45 MPH 36H 19/1200Z 13.9N 67.0W 45 KT 50 MPH 48H 20/0000Z 14.1N 70.9W 50 KT 60 MPH 72H 21/0000Z 14.8N 78.6W 60 KT 70 MPH 96H 22/0000Z 16.0N 85.5W 60 KT 70 MPH 120H 23/0000Z 17.5N 89.0W 55 KT 65 MPH...INLAND $$ Forecaster Pasch

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Priorities Discussion Worksheet (PDF)

2017-08-17 22:50:49| PortlandOnline

PDF Document, 74kbCategory: May 30, 2017 - Meeting 3

Tags: pdf discussion priorities worksheet

 

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