630
WTNT41 KNHC 192048
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