ZCZC MIATCDEP2 ALL
TTAA00 KNHC DDHHMM
 
Hurricane Norma Discussion Number   5
NWS National Hurricane Center Miami FL       EP172023
300 PM MDT Wed Oct 18 2023
 
Norma continues to rapidly intensify this afternoon. Intense 
inner-core convection has resulted in a ring of very cold cloud tops 
surrounding the center of the cyclone, and a ragged eye has emerged 
in recent visible images of Norma. The latest subjective Dvorak 
classifications from TAFB and SAB were T4.5/77 kt and T4.0/65 kt, 
respectively, and the UW-CIMSS objective ADT and AiDT estimates are 
around 70 kt. The initial intensity is raised to 70 kt based on a 
blend of these data, which makes Norma a hurricane.

Norma has rapidly strengthened by 30 kt during the past 24 h. The 
warm waters, weak to moderate vertical shear, and moist and unstable 
environment around Norma appear favorable for more steady to rapid 
strengthening through early Thursday. The NHC forecast closely 
follows the regional hurricane models in the near term and shows 
Norma becoming a major hurricane on Thursday. Thereafter, an 
increase in southwesterly shear should begin to disrupt the vertical 
structure of Norma and cause some weakening on Friday and through 
the weekend. The NHC forecast lies on the higher end of the 
guidance, closest to HCCA, during the latter part of the period. 

Recent microwave and scatterometer fixes indicate that Norma is 
moving northward (350/7 kt). A northward to north-northwestward 
motion is expected for the next couple of days or so while the storm 
moves around a weak ridge to its east. The track models are in good 
agreement on this part of the forecast, and the updated NHC track 
forecast is faster than the previous one through 72 h, following the 
latest HCCA aid. There remains a significant spread in the track 
guidance at days 3-5. The GFS and regional hurricane models (HAFS, 
HWRF, HMON) show a northward motion near the southern tip of Baja 
this weekend, followed by a northeastward motion toward the coast of 
western Mexico. Other global models (ECMWF, UKMET, Canadian) show a 
shallower Norma stalling or meandering to the southwest of Baja. The 
vertical depth and structure of Norma will likely play a major role 
in its long-term track, and there is above average uncertainty in 
this part of the track forecast. For now, the NHC forecast remains 
closer to the stronger GFS-based guidance, although not as fast as 
the deterministic GFS solution.

Given the uncertainty described above, it is difficult to pinpoint 
the extent or magnitude of potential impacts to portions of Baja 
California or western Mexico over the weekend. Interests in these 
areas should closely monitor the latest forecast updates, as more 
significant track or intensity adjustments could be required in 
future advisories.
 
 
Key Messages:
 
1. Norma is forecast to continue rapidly strengthening through 
Thursday while it passes well offshore of southwestern Mexico.
 
2. There remains 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 and western Mexico. 
Regardless, 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 tonight or on Thursday.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/2100Z 15.6N 108.0W   70 KT  80 MPH
 12H  19/0600Z 16.6N 108.1W   85 KT 100 MPH
 24H  19/1800Z 17.7N 108.3W  100 KT 115 MPH
 36H  20/0600Z 18.7N 108.7W   95 KT 110 MPH
 48H  20/1800Z 19.6N 109.1W   85 KT 100 MPH
 60H  21/0600Z 20.8N 109.7W   75 KT  85 MPH
 72H  21/1800Z 22.1N 110.0W   70 KT  80 MPH
 96H  22/1800Z 22.7N 109.9W   65 KT  75 MPH
120H  23/1800Z 24.0N 109.0W   50 KT  60 MPH
 
$$
Forecaster Reinhart
 
NNNN