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Tropical Depression Emily Forecast Discussion Number 7

2017-08-01 16:40:52| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Tue Aug 01 2017 000 WTNT41 KNHC 011440 TCDAT1 Tropical Depression Emily Discussion Number 7 NWS National Hurricane Center Miami FL AL062017 1100 AM EDT Tue Aug 01 2017 After an earlier convective hiatus, recent satellite, radar, and lightning data indicate that thunderstorm activity has redeveloped within 20 nmi of the low-level center. Although the small circulation is somewhat elongated northeast-to-southwest, I am hesitant to discontinue advisories on Emily at this time in case the new convection persists. Buoy 41010 southeast of the center has been reporting sustained winds of 25-29 kt at a 4-meter elevation early this morning, but the initial intensity will remain at 25 kt since convection has only recently redeveloped. Emily has made the anticipated turn toward the northeast and is now moving 050/12 kt. The depression is embedded in southwesterly flow ahead of an eastward-moving, deep-layer trough and frontal system. Emily is forecast to accelerate northeastward over the western Atlantic through the remainder of the forecast period, remain well offshore of the southeast and east coasts of the United States. The new official forecast track lies close to the previous advisory track, and is between the HCCA and TVCN consensus models. Emily is expected to remain ahead of a cold front for the next 24 hours or so, which could allow for some slight strengthening while the southwesterly vertical wind shear remains in the 10-15-kt range. Thereafter, the shear is forecast to steadily increase, exceeding 30 kt by 60 h, resulting in Emily becoming an extratropical or post-tropical remnant low by 36-48 hours. The NHC intensity forecast is identical to the previous advisory, and is similar to the the consensus model IVCN and guidance provided by the NOAA Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 29.3N 78.9W 25 KT 30 MPH 12H 02/0000Z 30.4N 77.5W 30 KT 35 MPH 24H 02/1200Z 32.1N 75.1W 30 KT 35 MPH 36H 03/0000Z 33.9N 72.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 48H 03/1200Z 35.3N 68.8W 30 KT 35 MPH...POST-TROP/EXTRATROP 72H 04/1200Z 37.6N 62.2W 30 KT 35 MPH...POST-TROP/EXTRATROP 96H 05/1200Z 39.0N 55.5W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 06/1200Z...DISSIPATED $$ Forecaster Stewart

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Tropical Depression Irwin Forecast Discussion Number 41

2017-08-01 16:40:30| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Tue Aug 01 2017 000 WTPZ45 KNHC 011440 TCDEP5 Tropical Depression Irwin Discussion Number 41 NWS National Hurricane Center Miami FL EP102017 800 AM PDT Tue Aug 01 2017 Irwin basically consists of a tight swirl of low clouds devoid of deep convection. Dvorak numbers have continued to decrease, and assuming that winds have diminished since the last ASCAT pass about 8 hours ago, the initial intensity is set at 30 kt. The cyclone is already moving over cold waters of about 22 deg C. On this basis, weakening should continue, and Irwin is anticipated to become a remnant low this afternoon. Irwin is moving toward the north-northwest or 335 degrees at 9 kt. A gradual turn toward the northwest is expected today as the cyclone becomes a shallow system steered by the low-level flow. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 25.9N 129.2W 30 KT 35 MPH 12H 02/0000Z 27.0N 130.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 02/1200Z 28.0N 131.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 03/0000Z 29.0N 132.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 03/1200Z...DISSIPATED $$ Forecaster Avila

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Tropical Storm Irwin Forecast Discussion Number 40

2017-08-01 10:54:22| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Tue Aug 01 2017 000 WTPZ45 KNHC 010854 TCDEP5 Tropical Storm Irwin Discussion Number 40 NWS National Hurricane Center Miami FL EP102017 200 AM PDT Tue Aug 01 2017 Irwin stubbornly remains a tropical cyclone this morning. The systems continues to produce a small area of deep convection near the center despite being over SSTs of around 22 deg C. The convection has gradually waned over the past 24 hours, but recent ASCAT data indicate that the maximum winds remain around 40 kt. Irwin should lose all of its remaining convection later today, and should become post-tropical within the next 12 to 24 hours while it moves over even colder waters. As a result, the system is forecast to gradually spin down, with the remnant circulation dissipating in 2 to 3 days. A mid-level high pressure area to the northeast of Irwin continues to steer the cyclone north-northwestward. This general motion is forecast to continue this morning. As Irwin weakens and becomes a shallow system, it should slow down and turn northwestward. The track guidance remains in agreement on this scenario and no significant change to the previous forecast was required. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 24.9N 128.8W 40 KT 45 MPH 12H 01/1800Z 26.2N 129.7W 30 KT 35 MPH 24H 02/0600Z 27.5N 130.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 02/1800Z 28.4N 131.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 03/0600Z 29.2N 132.6W 15 KT 15 MPH...POST-TROP/REMNT LOW 72H 04/0600Z...DISSIPATED $$ Forecaster Brown

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Tropical Depression Emily Forecast Discussion Number 6

2017-08-01 10:35:54| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Tue Aug 01 2017 000 WTNT41 KNHC 010835 TCDAT1 Tropical Depression Emily Discussion Number 6 NWS National Hurricane Center Miami FL AL062017 500 AM EDT Tue Aug 01 2017 Radar and surface observations over east-central Florida indicate that Emily's circulation has become quite elongated. Water vapor imagery also shows that drier mid-level air has moved over the northwestern portion of the circulation, which has limited the amount of convection near the center overnight. Some deep convection is noted along a trough axis well to the northeast of Emily. Earlier ASCAT data revealed a few 20-25 kt wind vectors just off the coast of Florida to the southeast of the center, so the initial intensity remains 25 kt for this advisory. Emily has been moving east-northeastward overnight. The cyclone remains embedded within the base of a mid-level trough that extends southwestward just off the southeastern United States coast. As this trough lifts out, Emily should accelerate northeastward between the western Atlantic ridge and another mid-level trough that will approach the southeast United States in a day or so. The global models shifted slightly westward this cycle, and the new NHC track has been nudged in that direction. The intensity forecast remains quite uncertain. Since Emily's circulation has become less defined and is near a weak frontal zone, it is possible that that system will be absorbed within the larger trough axis. For now, the NHC forecast assumes that Emily will maintain its identity and have a chance to restrengthen over the western Atlantic. Although the shear is not forecast to be prohibitive during the next day or so, the current structure and nearby dry air suggest any deepening should be slow to occur. This is supported by the global models which do not indicate much intensification. The NHC forecast is a little below the previous advisory and is close to guidance provided by the NOAA Ocean Prediction Center. Emily is forecast to become extratropical in about 36 hours, but it could dissipate or become post-tropical sooner than that. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 28.3N 80.1W 25 KT 30 MPH 12H 01/1800Z 29.4N 78.6W 25 KT 30 MPH 24H 02/0600Z 31.0N 76.5W 30 KT 35 MPH 36H 02/1800Z 32.8N 73.6W 30 KT 35 MPH...POST-TROP/EXTRATROP 48H 03/0600Z 34.4N 70.4W 30 KT 35 MPH...POST-TROP/EXTRATROP 72H 04/0600Z 37.0N 64.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 96H 05/0600Z 38.5N 57.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 06/0600Z...DISSIPATED $$ Forecaster Brown

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Tropical Depression Emily Forecast Discussion Number 5

2017-08-01 04:43:49| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Mon Jul 31 2017 000 WTNT41 KNHC 010243 TCDAT1 Tropical Depression Emily Discussion Number 5 NWS National Hurricane Center Miami FL AL062017 1100 PM EDT Mon Jul 31 2017 Mesonet observations from the area north and northwest of Lake Okeechobee indicate that Emily has an elongated surface circulation. Although some deep convection has redeveloped near and to the east of the center, Doppler velocity data from the Tampa and Melbourne WSR-88D radars only show winds of 30-35 kt at an elevation of about 5000 ft. Therefore, Emily's maximum sustained surface winds are estimated to be 25 kt, primarily within the thunderstorm activity east and southeast of the center. Emily's center, as seen on radar, has been moving east-southeastward for much of the evening. However, it seems to have recently turned eastward, and the initial motion estimate is 095/8 kt. Emily is embedded within the base of a mid-level trough that lies off the southeastern coast of the United States, and the subtropical ridge to the east should cause the cyclone to turn northeastward soon, move off the east-central Florida coast early Tuesday, and then accelerate over the western Atlantic during the next several days. Although all of the track models agree on this scenario, the GFS is a notable outlier compared to the other models, showing a slower solution that leans more to the left. Because the other models are so tightly clustered, the updated NHC track forecast leans closer to them and is a little bit faster than the previous forecast. There is low confidence in how strong Emily will get, or what exactly it will be, during the next few days. The global models keep Emily embedded within or near a weak frontal zone while it moves across the western Atlantic, suggesting that the cyclone's center may not move continuously but rather jump and reform from time to time along the boundary. These models also do not show Emily restrengthening much, even over the warm ocean, and phase-space diagrams suggest that the cyclone may become more cold core during the next few days. On the other hand, the more tropical models, like SHIPS and HWRF, show a little bit more re-intensification. Given that vertical shear is forecast to increase, and that Emily likely isn't purely tropical to begin with, the new NHC intensity forecast sides with the global models just a little bit more than SHIPS and HWRF. Based on this, Emily is forecast to intensify just a bit and become extratropical in about 48 hours. The extratropical low is expected to dissipate by day 5. The primary threat with Emily continues to be locally heavy rainfall across portions of the southern Florida peninsula and the Florida Keys overnight. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 27.5N 81.0W 25 KT 30 MPH...INLAND OVER FLORIDA 12H 01/1200Z 28.7N 79.2W 30 KT 35 MPH...OVER WATER 24H 02/0000Z 30.4N 77.0W 30 KT 35 MPH 36H 02/1200Z 32.1N 74.6W 30 KT 35 MPH 48H 03/0000Z 33.7N 71.8W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 04/0000Z 36.6N 65.7W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 05/0000Z 38.5N 58.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 06/0000Z...DISSIPATED $$ Forecaster Berg

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