####018004151####
WTPZ42 KNHC 190252

TCDEP2

 

Hurricane Norma Discussion Number   6

NWS National Hurricane Center Miami FL       EP172023

900 PM MDT Wed Oct 18 2023

 

Norma's rapid intensification continues. Microwave imagery from late 

this afternoon indicated that a very well-defined low- to mid-level 

eye has formed with a surrounding ring of shallow to moderate 

convection associated with rapid intensification. While that eye is 

not yet visible in conventional satellite imagery, subjective 

Dvorak estimates from TAFB and SAB have increased to 77 kt and 90 

kt, respectively, while recent objective evaluations from UW-CIMSS 

range from about 75 kt to 85 kt. Based on the whole of the data, 

the intensity for Norma has been raised to 80 kt.

 

For the next 24 to 36 hours, the forecast for Norma appears to be 

relatively straightforward. Continued rapid strengthening appears 

likely tonight based on Norma's convective structure and the 

conducive surrounding environment. The hurricane should continue 

moving generally northward during that time, steered by a weak 

mid-level ridge to the east of Norma and an upper-level trough to 

its northwest. Short-term fluctuations in intensity due to eyewall 

replacement cycles will become possible starting tonight, but 

confidence in the forecast is reasonably high through 36 h.

 

After that time, the uncertainty grows considerably. Southwesterly 

upper-level flow associated with the aforementioned upper-level 

trough will continue, but the mid- to lower-level steering will 

likely become light or even switch to northerly. The resulting 

increase in shear should cause Norma to weaken, but the rate of that 

weakening remains in doubt. As long as the hurricane retains its 

vertical depth, upper-level flow should keep it moving northward. 

However, once Norma weakens to the point that its steering is 

dominated by low- to mid-level flow, its forward speed should slow 

down considerably. It is possible, therefore, that Norma will stall 

just south of Baja California peninsula, a solution favored by the 

deterministic ECMWF and a number of its ensemble members. However, 

the hurricane models (HAFS-A/B, HMON, and HWRF), which should 

resolve the structure of Norma better than a global model, all 

indicate that the hurricane will retain its depth long enough to 

reach the Baja California peninsula. The NHC track and intensity 

forecasts favor the regional models, blending their latest consensus 

with the previous forecast to try to maintain continuity. The 

updated official track forecast is slightly faster than the previous 

one, but is generally similar despite the high uncertainty.



Tropical storm or hurricane watches could be required for portions 

of the Baja California peninsula later tonight, and interests there 

should continue to monitor updates on Norma, especially since 

larger-than-normal changes to the forecast are possible due to the 

high uncertainty in this case.

 

Key Messages:

 

1. Norma is forecast to continue rapidly strengthening tonight

while it passes well offshore of southwestern Mexico.

 

2. There is a greater than normal uncertainty in the track and

intensity forecasts for Norma later this week and this weekend when

it is expected to approach the Baja California peninsula and

western Mexico. Regardless of Norma's exact track or intensity,

there is an increasing threat of wind and rainfall impacts to

southern portions of Baja California Sur by Saturday, and watches

could be required there later tonight or on Thursday.

 

 

FORECAST POSITIONS AND MAX WINDS

 

INIT  19/0300Z 16.4N 108.0W   80 KT  90 MPH

 12H  19/1200Z 17.2N 108.1W  100 KT 115 MPH

 24H  20/0000Z 18.3N 108.4W  100 KT 115 MPH

 36H  20/1200Z 19.3N 108.9W   90 KT 105 MPH

 48H  21/0000Z 20.6N 109.5W   80 KT  90 MPH

 60H  21/1200Z 22.1N 109.8W   70 KT  80 MPH

 72H  22/0000Z 23.0N 109.8W   65 KT  75 MPH

 96H  23/0000Z 23.5N 109.5W   60 KT  70 MPH

120H  24/0000Z 24.0N 108.5W   45 KT  50 MPH

 

$$

Forecaster D. Zelinsky