ZCZC MIATCDEP5 ALL
TTAA00 KNHC DDHHMM
 
Tropical Storm Ignacio Discussion Number   5
NWS National Hurricane Center Miami FL       EP102021
300 PM MDT Mon Aug 02 2021
 
Ignacio appears to have peaked in intensity, with moderate-to- 
strong northeasterly vertical wind shear having displaced most of 
the deep convection into the southwestern semicircle of the 
cyclone. The latest subjective satellite current intensity 
estimates from TAFB and SAB remain at T2.5/35 kt, and objective 
estimates from UW-CIMSS ADT and SATCON are 37 kt and 38 kt, 
respectively. Based on these data, the intensity has been held at 
35 kt, which could be generous. The center of Ignacio passed 15-20 
nmi northeast of Clarion Island, Mexico, where the pressure fell to 
1006.5 mb around 1400 UTC and the highest winds measured were 
sustained 22 kt gusting to 33 kt according to a Mexican navy 
observing station on the island. A pronounced wind shift from the 
northeast to the southwest and west was also noted in the wind 
data. However, wind speeds have been steadily decreasing over the 
past several hours, an indication that the strongest winds are 
likely occurring in the northeastern quadrant. Unfortunately, all 
three ASCAT passes again missed the center and the strongest winds 
associated with Ignacio.
 
The initial motion estimate is 300/08 kt. No significant changes 
were required to the previous track forecast. Ignacio is forecast to 
maintain a west-northwestward motion between a strong 
mid-/upper-level ridge to the north and Hurricane Hilda to the 
southwest throughout the short forecast period. The new advisory 
track forecast is similar the previous forecast track, and lies 
along the left side of the consensus track models envelope.
 
Ignacio is expected to gradually weaken during the next 48 hours due 
to steadily increasing northeasterly vertical wind shear in excess 
of 25 kt by 24 hours and beyond. By 18-24 hours, Ignacio will be 
moving over sub-26C sea-surface temperatures, which will act to 
hasten the weakening process, with dissipation expected by 60 hours, 
if not sooner. The new NHC intensity forecast is similar to the 
previous advisory and a blend of the NOAA-HCCA and IVCN consensus 
intensity models.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  02/2100Z 18.8N 114.9W   35 KT  40 MPH
 12H  03/0600Z 19.5N 116.0W   30 KT  35 MPH
 24H  03/1800Z 20.4N 117.2W   25 KT  30 MPH
 36H  04/0600Z 21.2N 118.1W   20 KT  25 MPH...POST-TROP/REMNT LOW
 48H  04/1800Z 21.2N 118.9W   20 KT  25 MPH...POST-TROP/REMNT LOW
 60H  05/0600Z...DISSIPATED
 
$$
Forecaster Stewart
 
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