Tropical Storm Norma Forecast Discussion Number 4

NOAA - Tropical Weather Updates

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Issued at 900 AM MDT Wed Oct 18 2023

000
WTPZ42 KNHC 181455
TCDEP2
 
Tropical Storm Norma Discussion Number   4
NWS National Hurricane Center Miami FL       EP172023
900 AM MDT Wed Oct 18 2023
 
The satellite presentation of Norma this morning suggests the storm
is strengthening. Deep convection appears to be consolidating near
and over the estimated center of the tropical cyclone. A large
curved band of convection wraps around the eastern portion of its
circulation. The latest objective and subjective satellite estimates
range from 55-63 kt, and the initial intensity is raised to 60 kt
for this advisory. Scatterometer overpasses are expected later
today, which will help assess the structure and extent of Norma's
wind field.
 
In the near term, the atmospheric and oceanic conditions appear
favorable for continued strengthening. Norma is moving over very
warm (>29C) waters, within a moist and very diffluent upper-level
environment. With only weak to moderate deep-layer southerly shear
expected during the next 12-24 h, Norma should become a hurricane
soon. The statistical rapid intensification (RI) indices indicate RI
is more likely than not during the next 24 h, and the NHC intensity
forecast continues to explicitly show RI with Norma peaking as a
major hurricane in 24-36 h. Then, an increase in southwesterly shear
by this weekend should induce weakening through the rest of the
forecast period. The NHC intensity prediction was lowered at days
4-5 based on the increasingly hostile conditions depicted in the
latest guidance.
 
Norma is moving north-northwestward (340/6 kt). This general motion
should continue for the next couple of days while the storm moves
around a weak ridge to its east. There is greater than normal
uncertainty in the track forecast beyond 48-60 h, with diverging
solutions among the various track models. Stronger models with a
deeper vortex, including the GFS and regional hurricane models, show
Norma turning northward to northeastward and passing near the
southern tip of Baja California before approaching mainland Mexico.
Some weaker solutions, such as the ECMWF and UKMET, suggest Norma
could meander offshore of Baja California within weak steering
currents or even turn southwestward away from land later in the
period. Given this large spread in the guidance, it seems prudent to
avoid making major track forecast changes this morning. Therefore,
the longer range NHC forecast is similar to the previous one, but
shows little net motion at days 4-5. Future advisories could
require more significant adjustments to the track forecast.
 
 
Key Messages:
 
1. Norma is forecast to become a hurricane later today and continue
strengthening through Thursday while it passes well offshore of
southwestern Mexico.
 
2. There is greater than normal uncertainty in the track and
intensity forecasts for Norma later this week and this weekend while
it approaches the Baja California peninsula. Regardless, Norma could
bring wind and rainfall impacts to southern portions of Baja
California Sur by Saturday, and interests there should monitor the
latest forecast updates.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/1500Z 14.8N 107.9W   60 KT  70 MPH
 12H  19/0000Z 15.8N 108.1W   75 KT  85 MPH
 24H  19/1200Z 16.9N 108.3W   90 KT 105 MPH
 36H  20/0000Z 17.8N 108.5W  100 KT 115 MPH
 48H  20/1200Z 18.7N 109.0W   90 KT 105 MPH
 60H  21/0000Z 19.6N 109.5W   85 KT 100 MPH
 72H  21/1200Z 20.8N 109.9W   75 KT  85 MPH
 96H  22/1200Z 21.9N 109.9W   65 KT  75 MPH
120H  23/1200Z 22.5N 109.5W   55 KT  65 MPH
 
$$
Forecaster Reinhart
 

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