Tropical Storm Olaf Discussion Number 12
NWS National Hurricane Center Miami FL EP152021
900 AM MDT Fri Sep 10 2021
The satellite presentation of Olaf has significantly degraded over
the past several hours after the center moved across the southern
portion of Baja California Sur overnight. The system's organized
convection has collapsed, and infrared satellite imagery indicates
cloud top temperatures are rapidly warming near the estimated center
position. The initial intensity is lowered to 60 kt for this
advisory, which now makes Olaf a tropical storm. This estimate may
still be generous, but limited surface observations and radar data
make it difficult to confidently assess the intensity. Hopefully,
scatterometer data this afternoon will provide more insight into
changes in Olaf's surface wind field.
The tropical storm has slowed down a bit since last night, and its
estimated motion is northwest (310 degrees) at 9 kt. Recent
microwave imagery suggests the center of Olaf is just offshore the
southwestern coast of Baja California Sur, and the cyclone is likely
to move roughly parallel to the coast today. Then, a strong
mid-level high pressure ridge centered over the southern Rockies is
expected to build westward to the north of Olaf. This ridge should
turn Olaf toward the west by tonight, and then toward the southwest
through early next week. The official NHC track forecast has been
adjusted to the south of the previous forecast once again, in
agreement with the latest multi-model consensus aids.
Olaf is likely to continue rapidly weakening during the next couple
of days. In the short-term, its proximity to the mountainous terrain
of the Baja California peninsula will disrupt its ability to sustain
organized convection. As Olaf moves away from land, the cyclone will
encounter decreasing sea-surface temperatures and very dry mid-level
air, which should expedite its transition into a post-tropical
cyclone. In fact, the latest GFS and ECMWF model simulated satellite
imagery show Olaf becoming completely devoid of convection within
the next 24-36 h. The latest NHC intensity forecast shows more rapid
weakening than the previous one, primarily based on recent satellite
trends and the lower initial intensity. The official forecast
remains below the HCCA and IVCN consensus aids, which are inflated
by the SHIPS and LGEM models that fail to weaken Olaf during the
next 24 h.
Key Messages:
1. Olaf is forecast to move along the southwestern coast of the
Baja California peninsula today, with tropical storm conditions
continuing over southern portions of Baja California Sur through
this evening. These winds should diminish tonight as Olaf continues
weakening and turns westward away from land.
2. Heavy rains associated with Olaf are expected across portions of
southern Baja California Sur through today. This will pose a threat
of significant and life-threatening flash flooding and mudslides.
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