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Tropical Depression Eight Forecast Discussion Number 3

2017-08-13 16:41:45| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Sun Aug 13 2017 000 WTNT43 KNHC 131441 TCDAT3 Tropical Depression Eight Discussion Number 3 NWS National Hurricane Center Miami FL AL082017 1100 AM EDT Sun Aug 13 2017 The overall organization of the depression has changed little this morning. Visible satellite imagery and NOAA buoy data indicate that center is located near the northwestern edge of the area of convective banding. In fact, nearly all of the convective banding is located over the eastern and southeastern portions of the circulation. The initial intensity remains 30 kt, which is supported by subjective Dvorak T-numbers of 2.0 from both TAFB and SAB. The depression is moving north-northwestward or 335/11 kt. The track forecast reasoning remains unchanged. The depression is forecast to move north-northwestward to northward around the western portion of a deep-layer subtropical ridge during the next day or so. After that time, the cyclone is expected to turn northeastward ahead of a shortwave trough that will be approaching the northeastern United States. As the southwesterly flow increases over the western Atlantic ahead of the trough by 72 hours, the cyclone should begin to accelerate northeastward. The track guidance is once again in excellent agreement, and only a slight westward adjustment from the previous forecast was required. The depression is currently over warm water and within a low shear environment, but the mid-level atmosphere is relatively dry. These conditions should allow some modest strengthening during the next day or so. Vertical shear is forecast to increase by late Monday, and increase further in 2 to 3 days, which should put an end to any additional intensification. The system is forecast to become extratropical in 3 to 4 days, but if it does not strengthen it could be absorbed by an approaching trough off the Mid-Atlantic and northeastern U.S. in a few days. The latter portion of the forecast continues to be based on guidance provided by the NOAA Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 13/1500Z 27.4N 71.5W 30 KT 35 MPH 12H 14/0000Z 29.1N 72.2W 35 KT 40 MPH 24H 14/1200Z 30.7N 72.4W 40 KT 45 MPH 36H 15/0000Z 32.5N 71.9W 45 KT 50 MPH 48H 15/1200Z 34.6N 70.5W 50 KT 60 MPH 72H 16/1200Z 39.0N 62.0W 50 KT 60 MPH 96H 17/1200Z 42.5N 49.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 18/1200Z 47.0N 35.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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Tropical Depression Jova Forecast Discussion Number 7

2017-08-13 16:38:46| Tropical Depression LIDIA

Issued at 800 AM PDT Sun Aug 13 2017

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Tropical Depression Eight Forecast Discussion Number 2

2017-08-13 10:52:45| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sun Aug 13 2017 000 WTNT43 KNHC 130852 TCDAT3 Tropical Depression Eight Discussion Number 2 NWS National Hurricane Center Miami FL AL082017 500 AM EDT Sun Aug 13 2017 Satellite-derived winds from ASCAT passes at 0122Z and 0208Z indicated that the tropical depression had a closed surface circulation with peak winds of 33 kt in the southeastern quadrant. However, those peak winds were occurring in the same area of the circulation where NOAA Buoy 41046, which several hours ago measured a sustained wind of 35 kt and a peak gust to 43 kt, due to what appears to have been cold, downdraft-driven wind gusts based on a sharp decrease in the temperature and dew point values. As a result, the intensity will be held at 30 kt for this advisory, in line with a consensus 30-kt estimate from TAFB, SAB, and UW-CIMSS ADT. The initial motion estimate is 335/12 kt. The depression is forecast to move north-northwestward to northward for the next 36 h around the western portion a deep-layer subtropical ridge that is oriented east-west along 30-32N latitude. By 48 h and beyond, a vigorous shortwave trough currently located over the northern Plains is expected to dig east-southeastward and weaken the ridge along the east coast of the United States from the Carolinas northward to New England. The increasing southwesterly flow ahead of the trough is forecast to accelerate the cyclone northeastward, on an optimal track about midway from the U.S. and Bermuda and keeping it away from those two land masses. The new NHC tack forecast is similar to the previous advisory, and lies close to a blend of the HCCA and TVCN consensus track models. The depression is expected to remain in a relatively low vertical wind shear environment for the next 24-36 hours, but also within a fairly dry mid-level moisture environment for the duration of the forecast. As a result, only modest strengthening is expected during the next couple of days. By 48 h and beyond, southwesterly vertical wind shear is expected to steadily increase to more than 20 kt ahead of the aforementioned shortwave trough, reaching 40-50 kt by 96-120 h, which should act to cap any additional intensification. Owing to the strong shear, the cyclone is forecast to become extratropical by days 4 and 5. The official intensity forecast is similar to the previous advisory, and lies close to the consensus models IVCN and ICON. The intensity forecast at 96 and 120 h reflects guidance provided by the NOAA Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 26.5N 70.9W 30 KT 35 MPH 12H 13/1800Z 28.1N 71.7W 35 KT 40 MPH 24H 14/0600Z 29.9N 72.2W 40 KT 45 MPH 36H 14/1800Z 31.5N 72.0W 45 KT 50 MPH 48H 15/0600Z 33.4N 71.0W 50 KT 60 MPH 72H 16/0600Z 37.7N 64.1W 50 KT 60 MPH 96H 17/0600Z 42.4N 50.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 18/0600Z 46.3N 36.5W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Tropical Depression Jova Forecast Discussion Number 6

2017-08-13 10:45:48| Tropical Depression LIDIA

Issued at 200 AM PDT Sun Aug 13 2017

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Tropical Depression Eight Forecast Discussion Number 1

2017-08-13 04:48:22| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sat Aug 12 2017 000 WTNT43 KNHC 130248 TCDAT3 Tropical Depression Eight Discussion Number 1 NWS National Hurricane Center Miami FL AL082017 1100 PM EDT Sat Aug 12 2017 Late afternoon GOES-16 visible satellite images showed that the circulation associated with the low pressure located northeast of the Bahamas had become better defined. Since that time, the night-time microphysics RGB product and other infrared satellite pictures have continued to show an improvement in the circulation, and recent ASCAT data show that the system has acquired a well- defined center. Deep convection is organized in a large curved band, however the center is located near the western edge of the band. NOAA buoy 41046 located southeast of the center reported 25 to 30 kt winds earlier this evening, and the scatterometer data support an initial wind speed of 30 kt. The depression is moving north-northwestward or 330/11 kt. The depression should move north-northwestward to northward around the western side of a deep-layer ridge over the central Atlantic through Sunday night. It is expected to reach the mid-latitude westerlies by late Monday and begin to accelerate northeastward ahead of a short-wave trough that will be approaching the northeastern United States. The steering currents are well established over the western Atlantic and the track guidance is in good agreement on the forecast scenario. The NHC track forecast lies near the various consensus aids. The intensity forecast is more problematic. The system is expected to traverse warm water and remain in a low-shear environment during the next day or so, but intrusions of dry mid-level air are likely to limit strengthening. The statistical guidance and the HWRF favor more significant intensification than the global models, which generally do not show much deepening. In deference to the global models, the NHC forecast is below the consensus, especially later in the period. The system is likely to become extratropical in 3 to 4 days, and the extratropical portion of the forecast is based on guidance provided by the NOAA Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 25.3N 70.3W 30 KT 35 MPH 12H 13/1200Z 27.0N 71.2W 35 KT 40 MPH 24H 14/0000Z 29.0N 71.9W 40 KT 45 MPH 36H 14/1200Z 30.7N 72.0W 45 KT 50 MPH 48H 15/0000Z 32.2N 71.4W 50 KT 60 MPH 72H 16/0000Z 36.2N 66.9W 55 KT 65 MPH 96H 17/0000Z 41.5N 54.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 18/0000Z 45.5N 39.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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