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Tropical Depression JULIA Forecast Discussion Number 20
2016-09-18 22:32:58| National Hurricane Center (Atlantic)
Issued at 500 PM EDT SUN SEP 18 2016 000 WTNT41 KNHC 182032 TCDAT1 TROPICAL DEPRESSION JULIA DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112016 500 PM EDT SUN SEP 18 2016 Julia's low-level circulation has continued to improve despite the lack of organized deep convection near the well-defined center. However, some tight curved banding features consisting of shallow to moderate convection have developed within 100 nmi of the center during the past few hours, a hint that the mid-level moisture is beginning to increase. The initial intensity remains 25 kt based on on a TAFB intensity estimate of T1.5/25 kt, and a 1535Z ASCAT pass that showed some surface winds near 25 kt just north of the center. Julia is moving northwestward or 330/06 kt. The cyclone is forecast to slow down and gradually turn toward the north-northwest and north later tonight. A northward motion is then expected to persist, ahead of a strong shortwave trough that is forecast to move toward the western Carolinas, until Julia moves near or just onshore the the southeastern coast of North Carolina on Tuesday. After that time, it is uncertain whether or not a weakening Julia will lift out to the northeast and merge with a frontal boundary, or drift southwestward as a remnant low. Regardless of the status of Julia by 72 hours, the models are in good agreement that the system will not be a tropical cyclone at that time or thereafter due to strong vertical wind shear and land interaction. The official track forecast is similar to the previous advisory, which is a compromise of the various global and regional model solutions. Julia has a narrow window of opportunity to strengthen tonight and Monday morning when the vertical wind shear is forecast to weaken significantly and the upper-level flow is expected to become more anticyclonic. These more conducive dynamics are forecast to coincide with the nighttime convective maximum period and also during the time when Julia will be over the Gulf Stream where SSTs are 29-30C. Buoy reports offshore the South Carolina coast indicate that surface dew points have increased to near 80F, a further indication that the atmosphere surrounding Julia is becoming more conducive for regeneration of convection near the center later tonight. By Monday afternoon and evening, increasing southwesterly shear ahead of the aforementioned shortwave trough should induce steady weakening, which is expected to continue as the cyclone approaches the coast of North Carolina. The intensity forecast remains unchanged is a little below the consensus model IVCN. However, due to the possibility that Julia could be a little stronger than currently expected, an Air Force Reserve Hurricane Hunter aircraft has tentatively been tasked to investigate the cyclone Monday afternoon. The primary threat from Julia will be locally heavy rainfall from eastern North Carolina northward to the Mid-Atlantic states and the northeastern U.S. when moisture from the cyclone, or its remnants, will interact with an approaching frontal system. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 32.3N 78.0W 25 KT 30 MPH 12H 19/0600Z 33.0N 78.0W 25 KT 30 MPH 24H 19/1800Z 34.0N 77.7W 30 KT 35 MPH 36H 20/0600Z 34.6N 77.5W 30 KT 35 MPH...INLAND 48H 20/1800Z 34.9N 77.5W 25 KT 30 MPH...INLAND 72H 21/1800Z 34.2N 78.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 22/1800Z...DISSIPATED $$ Forecaster Stewart
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