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Tropical Storm CARLOS

Tropical Storm Carlos Discussion Number   2...Corrected
NWS National Hurricane Center Miami FL       EP032021
800 PM PDT Sat Jun 12 2021

Corrected humidity value in third paragraph.
Satellite imagery indicates improved organization this evening as a 
cold convective burst has expanded over the estimated low-level 
circulation center. A 2032 UTC AMSR2 microwave pass indicated that 
underneath this convective burst was also improved convective 
banding, especially over the southern semicircle. The latest round 
of Dvorak satellite estimates were T2.0/30 kt from TAFB and T2.5/35 
kt from SAB. The most recent UW-CIMSS Advanced Dvorak Technique 
value was also T2.5/35 kt. Favoring the higher intensity estimates, 
and assuming some intensification has occurred from the earlier 
scatterometer passes, Tropical Depression Three-E has been upgraded 
to Tropical Storm Carlos with an advisory intensity of 35 kt.
Carlos appears to be gradually turning leftward and slowing down 
this evening, with the most recent estimated motion at 270/06 kt. 
The mid-level ridge north of Carlos is forecast to gradually weaken, 
shift northward, and then be replaced by a deep-layer trough that 
will essentially shut down the steering currents near the cyclone 
after 24 h. Between 36 to 48 h the motion of Carlos is likely to 
slow to a crawl, generally to the west-southwest. By 72 h, another 
mid-to-upper level trough digging in from the northwest will finally 
induce some northerly steering, helping Carlos to gradually 
accelerate to the north. The latest track forecast is a bit west of 
the previous NHC forecast owing to the current motion, but remains 
very close to the HFIP corrected consensus and TCVE track consensus. 
It should be noted that there remains large spread in the guidance 
on how quickly Carlos slows down, with the latest GFS forecast 
slowing down the cyclone almost immediately, while the CMC and ECMWF 
runs show a much faster track to the west-southwest.
The intensity forecast is tricky due to both the small size of the 
tropical cyclone and also the less than optimal environment 
surrounding the system. While deep-layer vertical wind shear is only 
expected to be low to moderate over the next 72 h, mid-level shear 
out of the north to northwest is a bit higher (15-25 kt) and could 
occasionally import very dry mid-level air from that direction. In 
fact, ECMWF-SHIPS mid-level humidity values gradually decrease to 
under 50 percent in the next 36 h. In addition, the very slow motion 
of Carlos expected between 24-72 h could potentially upwell cooler 
sea-surface temperatures than the current 27-28 C values along the 
forecast track. For this reason, the latest NHC intensity forecast 
is fairly conservative, forecasting a peak intensity of 45 kt 
between 24-60 h, which is close to the HFIP corrected consensus and 
peak intensity of the most recent HWRF run. Thereafter, as the storm 
begins to gain latitude, increasingly dry, stable air in addition to 
decreasing sea surface temperatures should lead to gradual weakening 
beyond 60 h.
INIT  13/0300Z 11.9N 124.5W   35 KT  40 MPH
 12H  13/1200Z 11.8N 125.5W   40 KT  45 MPH
 24H  14/0000Z 11.4N 126.5W   45 KT  50 MPH
 36H  14/1200Z 10.8N 127.2W   45 KT  50 MPH
 48H  15/0000Z 10.6N 127.4W   45 KT  50 MPH
 60H  15/1200Z 10.3N 127.7W   45 KT  50 MPH
 72H  16/0000Z 10.3N 128.0W   40 KT  45 MPH
 96H  17/0000Z 11.5N 128.1W   35 KT  40 MPH
120H  18/0000Z 13.5N 127.9W   30 KT  35 MPH
Forecaster Papin/Pasch