Tropical Cyclone Discussion

374
WTPZ44 KNHC 132037
TCDEP4
 
Tropical Storm Norbert Discussion Number  17
NWS National Hurricane Center Miami FL       EP142026
1100 AM HST Sun Sep 13 2026
 
Visible satellite imagery indicates that Norbert’s center has become 
exposed. The bulk of the convection is located on the south and east 
sides of the storm. Water vapor imagery shows that a good amount of 
dry air has penetrated into the core of the cyclone. The latest TAFB 
Dvorak fix estimated the intensity around 45 kt and the objective 
intensity estimates from UW-CIMSS are in the range of 32-39 kt. In 
addition, recent ASCAT pass shows that the strongest winds close to 
the center were around 37 kt. Therefore, the initial intensity has 
been lowered to 40 kt for this advisory.
 
The initial motion is estimated to be 290/11 kt. The storm is
expected to move west-northwestward to westward as it moves to the
south of a low- to mid-level subtropical ridge. The track guidance
continues to have good agreement on the general heading for this
storm. The current NHC track forecast has been nudged slightly to
north of the previous forecast track and remains close to the 
corrected multi-model consensus (HCCA) and the Google DeepMind 
(GDMI) ensemble mean.
 
More fluctuations in intensity are possible in the short term as 
Norbert remains in a marginal environment. The cyclone continues to 
contend with mid-level dry air intrusions and light west- 
southwesterly vertical wind shear.  After 12 h, the wind shear 
is expected to increase, which should result in a gradual weakening. 
Around 60 h, the simulated GFS and ECMWF satellite imagery shows 
that the cyclone should lose organized deep convection and it is 
therefore expected to become a post-tropical remnant low and then 
dissipate by around 72 h. The current NHC intensity forecast 
remains in line with the latest guidance including the HCCA and 
GDMI consensus guidance.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  13/2100Z 18.8N 134.0W   40 KT  45 MPH
 12H  14/0600Z 19.2N 136.0W   40 KT  45 MPH
 24H  14/1800Z 19.7N 138.6W   35 KT  40 MPH
 36H  15/0600Z 20.2N 141.4W   35 KT  40 MPH
 48H  15/1800Z 20.7N 144.0W   30 KT  35 MPH
 60H  16/0600Z 20.8N 146.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  16/1800Z...DISSIPATED