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| #1204343 (Received by flhurricane at: 4:54 PM 19.Oct.2024) TCDAT1 Hurricane Oscar Discussion Number 3 NWS National Hurricane Center Miami FL AL162024 500 PM EDT Sat Oct 19 2024 It is fair to say its been an unexpected day with regards to Oscar. After being upgraded to a tropical storm this morning, a resources-permitting Air Force Reconnaissance mission found that Oscar was much stronger than anticipated and in fact was a tiny hurricane, prompting the earlier special advisory at 18 UTC. Having these critical in-situ aircraft observations has been invaluable to diagnosing the current intensity of the storm, and we thank the crew for flying this mission on short notice this morning. It is worth noting that remote sensing satellite intensity estimates are currently much lower, with the highest objective estimate at 55 kt from a DMINT AMSR2 pass at 1830 UTC. For what its worth, ASCAT-B/C also hit the small core of Oscar, only showing a peak wind retrieval of 42 kt from both passes and only a handful of other retrievals with tropical-storm-force winds. The last Air Force Reconnaissance leg through Oscar found peak 700-mb flight level winds of 77 kt. A dropsonde released in the northeast eyewall also had a 150 m layer mean average wind of 85 kt with a surface wind gust of 82 kt. A blend of the flight level and dropsonde data supports a wind speed of 75 kt this advisory. The wind field of Oscar is very small, with hurricane-force winds only extending out 5 n mi from the center, with a blend of aircraft and scatterometer data suggesting tropical-storm-force winds only extending about 30 n mi, primarily in the northern semicircle. Oscar has maintained a westward motion today, with recon fixes indicating an estimated motion of 275/9 kt. This motion, with a subtle shift a little more south of due west is anticipated over the next 24-36 h. On the current track, Oscar will pass very near portions of the Turks and Caicos Islands and Southeastern Bahamas this evening and tonight, where a hurricane warning is in effect. The narrow mid-level ridge that is currently steering the system is soon expected to become eroded by a longwave trough slowly sagging southward across the northwestern Atlantic Ocean, resulting in Oscar slowing down and bending a bit south of due west. Thereafter, as the trough produces a more pronounced weakness north of the hurricane, Oscar will likely execute a very slow but sharp turn to the north and then northeast. However, this is still expected to bring Oscar close to or over parts of eastern Cuba, before turning back northeastward. The latest NHC forecast track is a little further east of the prior forecast, blending the consensus aids TVCA and HCCA with the ECMWF model, which has been one of the few models that has depicted Oscar with much vertical coherence. The intensity forecast for Oscar is tricky, due to both the very small inner-core wind field associated with the hurricane, and the fact that none of the guidance (either global models, or hurricane-regional models) is depicting the current intensity right now. The last set of aircraft observations suggest the pressure is at least not rapidly dropping, with the final dropsonde providing an estimate of 987 mb. The NHC intensity forecast will show a bit more intensification, but I suspect the tiny hurricane will be quite susceptible to the increasingly negative environmental conditions. SHIPS guidance indicates that northwesterly vertical wind shear increases above 20 kt after 24 h and above 30 kt beyond 60 h. Very dry mid-level air exists in that region upstream of Oscar, and the storm could weaken rather quickly from 36-60 h. As we saw today, small systems like Oscar are often prone to rapid intensity changes, either up or down. After 96 h, most of the guidance that is able to depict Oscar shows it ultimately being absorbed by the deep-layer trough in the northwestern Atlantic, and the latest forecast still shows Oscar dissipating by that time. Key Messages: 1. Oscar is expected to bring hurricane conditions to portions of the Turks and Caicos Islands and the southeastern Bahamas this evening and overnight, and could bring hurricane conditions to eastern Cuba during the next day or two. A Hurricane Warning is in effect for the Turks and Caicos and southeastern Bahamas, and a Hurricane Watch is in effect for portions of eastern Cuba. 2. Oscar is expected to produce a dangerous storm surge on the Turks and Caicos Islands beginning this evening. Minor coastal flooding is also possible along the north shore of Cuba later on Sunday. 3. Locally heavy rainfall is possible across the Turks and Caicos Islands and the southeastern Bahamas later today and tonight. These rains are expected to spread to eastern Cuba on Sunday. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 21.4N 71.1W 75 KT 85 MPH 12H 20/0600Z 21.2N 72.6W 80 KT 90 MPH 24H 20/1800Z 21.0N 74.1W 80 KT 90 MPH 36H 21/0600Z 20.9N 74.9W 75 KT 85 MPH 48H 21/1800Z 21.2N 75.6W 60 KT 70 MPH 60H 22/0600Z 21.9N 75.3W 50 KT 60 MPH 72H 22/1800Z 23.3N 74.2W 45 KT 50 MPH 96H 23/1800Z 26.1N 72.1W 45 KT 50 MPH 120H 24/1800Z...DISSIPATED $$ Forecaster Papin |
