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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