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| #1108477 (Received by flhurricane at: 5:02 AM 23.Sep.2022) TCDAT4 Tropical Depression Nine Discussion Number 1 NWS National Hurricane Center Miami FL AL092022 500 AM AST Fri Sep 23 2022 Convection this morning has increased primarily to the east of the area of low pressure we have been monitoring in the central Caribbean Sea, currently passing by to the north of Curacao island. The system already possessed a well-defined circulation for the last 12 to 18 hours, but it was only overnight that the ongoing convective activity was able to persist long enough near the center to be considered a tropical cyclone. The most recent satellite intensity estimate from TAFB was up to T2.5/35-kt. However the GOES-16 derived motion winds from the meso sector over the system have only been 25-30 kt in the 925-850 mb layer on the northeastern periphery of the circulation. In addition, buoy 42059 located to the northeast of the center has been reporting winds up to only 27-kt. The combination of all these data provide enough justification to upgrade this system to Tropical Depression Nine, with the initial winds set at 30 kt for this advisory. An Air Force Reserve Reconnaissance mission will be investigating the system later this morning to provide more in-situ information of the system's structure and intensity. The current motion right now is estimated to be off to the west-northwest at 290/12 kt. In the short-term, the depression is forecast to bend back more westward as a narrow east-to-west oriented mid-level ridge builds in behind the weakness left behind from Fiona. The current eastward displaced convection may also tug the broad center in that direction as well. However, after 48 hours, this ridge will start to decay as a longwave deep-layer trough over the eastern United States begins to amplify southward. This synoptic evolution should then allow the cyclone to begin gaining latitude, though the exact timing at which this occurs could be somewhat related to the vertical depth of the cyclone and how it interacts with a weak upper-level trough expected to be over the far western Caribbean in the day 3-4 time-frame. The model guidance early on is in fairly good agreement, but larger across-track spread begins to take shape by 48 hours, with the GFS and its ensemble mean located further south and west, and with the ECMWF and its ensemble mean located further north and east. The initial track forecast has decided to split the difference between these two model suites, and lies fairly close to the consensus aids TVCN and HCCA. There is still a healthy amount of uncertainty in the track forecast at the day 4-5 timeframe. Currently the structure of the depression is quite disheveled, with the low-level circulation mostly exposed, with deep convective activity displaced to its west-southeast. This structure is due to 25-30 kt of northeasterly 200-850 mb vertical wind shear caused from the equatorward outflow channel of Fiona, resulting in significant upper-level flow over the system. However, as the depression moves westward, it will move out form under this unfavorable flow and into a lighter upper-level northeasterlies. However, it may take time for the low-level center to become better aligned with the convective activity, and thus only slow intensification is forecast over the next 24-48 hours. After that period, most of the guidance shows environmental conditions becoming much more favorable as shear drops under 10 kt and the cyclone is over the warm 29-30 C waters of the northwestern Caribbean. Thereafter, potential land interaction with Cuba, and the potential for an increase in southerly shear at day 5 may cap off the intensity at the end of the forecast. The initial NHC forecast shows the depression intensifying up to a category 2 hurricane by the time it nears the coast of Cuba. Key Messages: 1. Tropical Depression Nine is expected to produce heavy rainfall and instances of flash flooding and possible mudslides in areas of higher terrain in Aruba, Bonaire, and Curacao. Heavy rains are also likely to spread into Jamaica and the Cayman Islands in the coming days. 2. The depression is expected to approach Jamaica and the Cayman islands as an intensifying tropical storm. Watches and warnings for these locations may be required in subsequent forecast cycles. 3. This system is forecast to approach western Cuba and enter the southeastern Gulf of Mexico by the end of the forecast period. Interests in Cuba and those along the Eastern Gulf Coast of the United States should closely monitor this system, though at this juncture forecast uncertainty remains fairly high. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 13.9N 68.6W 30 KT 35 MPH 12H 23/1800Z 14.4N 70.2W 35 KT 40 MPH 24H 24/0600Z 14.7N 72.6W 35 KT 40 MPH 36H 24/1800Z 14.8N 75.0W 35 KT 40 MPH 48H 25/0600Z 15.5N 77.1W 40 KT 45 MPH 60H 25/1800Z 17.0N 78.8W 55 KT 65 MPH 72H 26/0600Z 18.9N 80.5W 65 KT 75 MPH 96H 27/0600Z 22.6N 82.6W 90 KT 105 MPH...NEAR CUBA 120H 28/0600Z 26.0N 82.3W 95 KT 110 MPH $$ Forecaster Papin |
