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
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