Tropical Storm Carlotta Discussion Number 10
NWS National Hurricane Center Miami FL EP042018
1000 PM CDT Sat Jun 16 2018
Carlotta has surprised us this evening. Radar images from Acapulco,
Mexico, indicate that the storm has strengthened and its structure
has improved significantly. The radar data indicate that Carlotta
has a well-defined, but tiny, inner core and the eye has been
contracting during the past few hours. In addition, the radar
echoes in the eyewall has been getting stronger and more symmetric
around the eye. The initial wind speed is set to 55 kt, in
agreement with a Dvorak classification from TAFB.
Carlotta is very close to the coast of southern Mexico and, in
fact, the northern eyewall is partially onshore. Since the
storm is expected to interact with land and is forecast to move
inland overnight or Sunday morning, it appears unlikely that
Carlotta will strengthen much more. Once inland, fast weakening is
expected and Carlotta should dissipate over the high terrain of
Mexico Sunday night or early Monday.
The storm has moved more to the west than previous thought, likely
due to the influence of a narrow mid-level ridge to its north. The
new forecast is adjusted well to the west of the previous one, and
is in fair agreement with the latest consensus models.
Regardless of whether the center moves inland, the threat of heavy
rainfall and potential of life-threatening flash floods and
mudslides continue over the southern parts of Guerrero and Oaxaca.
The rainfall threat will be enhanced by moist southwesterly flow
over the southern Sierra Madre mountains of Mexico. For details,
please see products issued by your local weather office.
Tropical Depression Four-E Discussion Number 1
NWS National Hurricane Center Miami FL EP042018
400 PM CDT Thu Jun 14 2018
Overnight scatterometer data indicate that the circulation of the
system was open on the northwestern side. High-resolution GOES-16
1-min visible data indicate that the low is now closed, with a
well-enough defined circulation center. Since there is plenty of
banded convection, this system is being designated as a tropical
depression, and the initial wind speed of 30 kt is based off the
overnight scatterometer data.
The initial motion estimate is an uncertain 325/5 kt. A weak
mid-level ridge over Mexico is forecast to break down by tomorrow,
leaving the depression in an area of light steering currents. Much
of the model guidance linger the system just south of the coast of
Mexico for the next couple of days until the cyclone gets drawn
northward into a larger trough currently seen over the western Gulf
of Mexico. There is considerable uncertainty in the timing of this
poleward motion, however, with the UKMET, HMON, and COAMPS-TC models
faster than the rest of the guidance. This seems like a pretty
clear case of staying near the model consensus, given the weak
steering flow that makes it nearly impossible to choose one model
over another one. Thus, the official forecast shows a slow
northward motion, near the eastern Pacific model consensus TVCE, and
it should be emphasized that the forecast timing of landfall is
subject to large changes in the future.
The system is not particularly well organized at the moment, with a
few swirls seen in the visible imagery rotating around the larger
gyre. After the low consolidates, light-to-moderate shear with
very warm waters, and high mid-level humidity should lead to steady
intensification. This is a tricky forecast, however, since land is
so close to the north, which would prevent much strengthening. The
official forecast is a blend of the statistical-dynamical guidance
and the regional hurricane guidance, a bit lower than the model
consensus since the HWRF keeps the cyclone well offshore (unlike
the official prediction), leading to a stronger storm.
It has been an active early part of the eastern Pacific season.
This is the 2nd earliest 4th tropical cyclone on record in the
basin during the satellite era (1966-present), only 6 hours behind
the previous record in 1974.
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