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Tropical Storm Julian Forecast Discussion Number 3
2021-08-29 16:53:37| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sun Aug 29 2021 000 WTNT41 KNHC 291453 TCDAT1 Tropical Storm Julian Discussion Number 3 NWS National Hurricane Center Miami FL AL112021 1100 AM AST Sun Aug 29 2021 The system has become better organized this morning, with the low-level center located on the southwestern edge of a persistent mass of deep convection. A 1246 UTC ASCAT-B pass revealed an area of winds over 40 kt southeast of the center, so the system is upgraded to Tropical Storm Julian with maximum winds of 45 kt. Julian is accelerating toward the northeast (045/15 kt) in the flow to the south of a deep-layer area of low pressure located just east of Newfoundland. The storm is expected to move around the southeastern and eastern periphery of this large low during the next few days, accelerating further and turning toward the north by 48 hours. The track models are all in good agreement on this scenario, and the NHC track forecast is very close to the TVCA and HCCA consensus aids. This new forecast is also relatively unchanged from the previous advisory. Winds in the storm have increased faster than expected, even in the face of 20 kt of west-southwesterly shear. This shear is forecast to increase substantially in the coming days, with SHIPS diagnostics indicating it may reach magnitudes of 40-50 kt. However, the storm will still be moving over marginally warm waters around 26 degrees Celsius, and its fast motion and some baroclinic forcing could allow for additional strengthening during the next 12-24 hours. Nearly all the intensity models support some strengthening, and the NHC official forecast peaks the winds at 55 kt in 24 hours, roughly between the IVCN and HCCA solutions. Phase-space diagrams suggest that Julian will probably already be going through extratropical transition at that time, and it should be fully extratropical by 36 hours. Gradual weakening is anticipated after 24 hours, and the extratropical low is likely to dissipate over the north Atlantic by day 3. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 35.1N 46.8W 45 KT 50 MPH 12H 30/0000Z 36.9N 43.7W 50 KT 60 MPH 24H 30/1200Z 40.0N 39.7W 55 KT 65 MPH 36H 31/0000Z 43.6N 37.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 31/1200Z 48.0N 36.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 60H 01/0000Z 52.2N 38.2W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 01/1200Z...DISSIPATED $$ Forecaster Berg
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