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Tropical Storm Olaf Discussion Number 7
NWS National Hurricane Center Miami FL EP152021
300 AM MDT Thu Sep 09 2021
Olaf's convective canopy has been expanding somewhat and become a
little more circular since last evening with clouds tops as cold as
-80 degrees Celsius. Dvorak estimates have bounced up to T3.5 from
TAFB, SAB, and the UW-CIMSS ADT, and Olaf's maximum winds are
therefore now estimated to be 55 kt. Recent scatterometer data also
indicated that the tropical-storm-force wind field is a little
bigger than previously estimated.
Also with the help of the scatterometer data, Olaf's center appears
to have tracked a bit to the east, and the initial motion is
estimated to be north-northwestward, or 340/5 kt. This has been
the recent trend over the past day or so, with the motion having
a more northward component than anticipated--but not surprising
given what previous GFS model runs have been suggesting. A strong
mid-level high over the western United States is expected to
eventually force Olaf toward the northwest and then west, but
probably not soon enough to avoid impacts on the southern Baja
California peninsula. Mostly due to the adjusted initial position,
the track models--and the NHC official forecast--have again shifted
closer to the southern tip of the peninsula, with a closest approach
in about 24 hours. This updated forecast is very close to the HCCA
consensus aid and would be close enough for the core of the storm to
at least graze land. It's also concerning that the GFS, HMON, and
COAMPS-TC models are still to the right of the official forecast and
the other models and show Olaf's center potentially moving over the
southern tip of the peninsula in about 24 hours. Olaf should
finally begin to move westward away from the peninsula in about 48
hours.
Although satellite images and model analyses suggest that some
moderate westerly shear is undercutting the outflow layer, Olaf has
been able to strengthen nonetheless. If Olaf's center does not
move over the Baja California peninsula, the storm will have the
opportunity to strengthen for another 24-36 hours while ocean
waters are warm and deep-layer shear is low. Therefore, the new
NHC intensity forecast is near the upper end of the guidance
envelope and shows Olaf becoming a hurricane later today. Further
strengthening beyond what's shown in the official forecast is
possible, with rapid intensification indices now close to a 50
percent chance of a 25-kt increase in winds over the next 24 hours.
By 48 hours, colder waters should cause Olaf's convection to
decrease, and global models suggest it could degenerate to a
convection-less post-tropical low by day 3.
The updated track and intensity forecasts have necessitated the
issuance of a Hurricane Warning by the government of Mexico for
southern portions of Baja California Sur, and an extension of
Tropical Storm Warnings northward along both east and west coasts
of the peninsula.
Key Messages:
1. Olaf is forecast to strengthen to a hurricane later today and
then pass very near or over the southern portion of Baja California
Sur tonight and on Friday. Tropical storm conditions are expected
to begin within the hurricane warning area this afternoon, and
preparations should therefore be rushed to completion this morning.
2. Heavy rains associated with Olaf are possible across portions of
far southern Baja California Sur today through Friday. This will
pose a threat of flash flooding and mudslides.
FORECAST POSITIONS AND MAX WINDS
INIT 09/0900Z 20.5N 108.0W 55 KT 65 MPH
12H 09/1800Z 21.4N 108.6W 65 KT 75 MPH
24H 10/0600Z 22.6N 110.0W 70 KT 80 MPH
36H 10/1800Z 23.5N 111.7W 65 KT 75 MPH
48H 11/0600Z 23.7N 113.2W 50 KT 60 MPH
60H 11/1800Z 23.5N 114.5W 40 KT 45 MPH
72H 12/0600Z 23.1N 115.7W 35 KT 40 MPH...POST-TROPICAL
96H 13/0600Z 22.1N 118.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 14/0600Z 21.3N 121.7W 20 KT 25 MPH...POST-TROP/REMNT LOW
$$
Forecaster Berg
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