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Tropical Storm Lidia Discussion Number   1
NWS National Hurricane Center Miami FL       EP152023
300 AM MDT Tue Oct 03 2023

The system we have been monitoring for the last several days to the 
south of the coast of Mexico (Invest 98E) has become better 
organized early this morning. A small but growing burst of deep 
convection has formed near or just west of where the estimated 
center is, and some curved banding features are starting to take 
shape. In addition, we had two scatterometer passes between 04-05 
UTC, showing the system has developed a well-defined closed 
circulation, with winds between 30-35 kt along the western flank of 
the circulation. Subjective intensity estimates were T1.5 from TAFB 
And T2.0 from SAB. However, based primarily on the earlier satellite 
wind-data, advisories are being initiated on Tropical Storm Lidia 
with an initial intensity of 35 kt for this advisory.

Lidia's initial motion is somewhat uncertain since it only recently 
became well-defined, but it is estimated to be moving slowly to the 
west-northwest at 300/8 kt. This current motion is a result of the 
system moving along the southern extent of a mid-level ridge 
centered over Mexico and the western Gulf of Mexico. However, a mid- 
to upper-level trough located to its northwest is expected to erode 
this ridge somewhat, allowing the tropical cyclone to turn northwest 
or north-northwest in the next 24-48 hours. While the track guidance 
is in relatively good agreement on this initial poleward turn, the 
guidance spread increases quite dramatically after 48 hours, with 
uncertainty if this poleward motion continues, or if Lidia turns 
back westward as the trough lifts out and allows a mid-level ridge 
to build back in. For this initial track forecast, the NHC forecast 
favors the latest GFS and ECMWF global model solutions, which show a 
narrow ridge building back in, allowing for a slow westward turn by 
the end of the forecast period. This track forecast also lies 
between the simple consensus aid TVCE, and a blend of the GFS and 
ECMWF solutions (GFEX). 

For the intensity forecast, Lidia appears like it will have to deal 
with moderate easterly shear for the next several days, though the 
ECMWF-SHIPS has lower shear than the GFS-SHIPS. To complicate 
matters, the initial structure of Lidia appears rather small, 
potentially making the system prone to larger-than-usual changes in 
intensity, both up or down. Even though the shear may keep its 
intensity in relative check, other environmental factors are quite 
favorable, with sea-surface temperatures near 30 C, and ample 
mid-level moisture. In fact, with the lower shear, the ECMWF-SHIPS 
rapid intensification index (RII) shows a 31 percent chance of a 30 
kt increase in intensity in 24 hours, and a 57 percent chance of 55 
kt increase in 48 hours. However, the dynamical hurricane-regional 
model guidance is much more subdued, but they appear to be 
struggling to capture the current small structure of the system. 
Thus, the initial intensity forecast is a relative compromise, 
showing gradual intensification, with is higher than the 
regional-hurricane model guidance, but is lower than the ECMWF-based 
SHIPS and LGEM models. This initial forecast is somewhat higher than 
the consensus aids IVCN and HCCA early on, but they end up near the 
NHC intensity forecast by the end of the period. 

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  03/0900Z 11.8N 107.0W   35 KT  40 MPH
 12H  03/1800Z 12.7N 108.1W   40 KT  45 MPH
 24H  04/0600Z 13.6N 108.9W   45 KT  50 MPH
 36H  04/1800Z 14.4N 109.2W   50 KT  60 MPH
 48H  05/0600Z 15.2N 109.5W   55 KT  65 MPH
 60H  05/1800Z 15.5N 109.9W   60 KT  70 MPH
 72H  06/0600Z 15.7N 110.6W   65 KT  75 MPH
 96H  07/0600Z 15.7N 111.7W   65 KT  75 MPH
120H  08/0600Z 15.5N 113.5W   65 KT  75 MPH
 
$$
Forecaster Papin
 
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