ZCZC MIATCDEP5 ALL
TTAA00 KNHC DDHHMM
 
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
 
NNNN