Hurricane Kenneth Discussion Number 12
NWS National Hurricane Center Miami FL EP132017
200 AM PDT Mon Aug 21 2017
Kenneth has continued to rapidly intensify since the previous
advisory. The satellite presentation of the hurricane is quite
impressive, as a 15-nmi wide eye has become better defined while
the cloud tops of the surrounding ring of convection has cooled.
Dvorak intensity estimates range from T5.5 (102 kt) from SAB,
T6.0 (115 kt) from TAFB, to T6.3 (122 kt) from UW/CIMSS. Using a
blend of these estimates, the initial wind speed has been increased
to 115 kt, making Kenneth a category 4 hurricane on the
Saffir-Simpson Hurricane Wind Scale.
The hurricane is expected to peak in intensity very soon as it will
be moving over cooler waters and into a more stable air mass
later today. After that time, cooler sea surface temperatures and
less favorable thermodynamic conditions should cause steady
weakening. In 3 to 4 days, increasing southwesterly shear from an
upper-level trough along 140W and sub 23C SSTs should cause
Kenneth's deep convection to dissipate, resulting in the system
becoming a post-tropical cyclone. The NHC intensity forecast is
slightly higher than the previous one at 12 and 24 h due to the
higher initial intensity. After that time, the forecast is fairly
similar to the previous advisory, and is a blend of the various
intensity aids.
The initial motion estimate is west-northwest or 300 degrees at
9 kt. The track forecast reasoning remains the same as the
previous advisory, as Kenneth is expected to turn northwestward
today, then north-northwestward on Tuesday between a mid-level ridge
to its east and a developing cut-off low to the west. Kenneth
should slow down considerably later in the period when it becomes a
vertically shallow system and is steered by the weaker low-level
flow. There is very little spread in the track guidance, and the
updated official forecast is near the middle of the guidance
envelope, and very close to the previous NHC forecast.
Hurricane Kenneth Discussion Number 11
NWS National Hurricane Center Miami FL EP132017
800 PM PDT Sun Aug 20 2017
Kenneth has rapidly intensified into a major hurricane this
evening, as the eye has dramatically warmed and the surrounding
cloud tops of the eyewall have cooled. At 00Z, a blend of TAFB,
SAB, and ADT Dvorak classifications averaged maximum winds of
95 kt. However, the continued convective development in the last
three hours suggests that the advisory intensity be boosted to
100 kt, and even that may be conservative.
While the hurricane has shown an impressive evolution in the last
day, this should not continue much longer. Kenneth will reach the
26C SST isotherm with drier, less unstable air late Monday, and it
is anticipated that Kenneth will peak by then. In about three
days, the vertical shear will go up appreciably due to Kenneth
approaching an upper-level trough. The combination of the hostile
thermodynamics and shear should cause a steady weakening through
the forecast period. Kenneth's deep convection is likely to
dissipate in three to four days, signaling the system's
transformation to a post-tropical cyclone. The official intensity
forecast is substantially higher than previously in the short-term
due to the unanticipated rapid intensification, but similar for 36
hours and beyond. This prediction is closest to a blend of the HMON
dynamical model and the LGEM/SHIPS statistical models.
The hurricane is moving toward the west-northwest at 9 kt, steered
by a weak mid-level ridge to its northeast. Kenneth should
gradually turn toward the north-northwest during the next couple of
days at about the same rate of forward speed, as it rounds the
mid-level ridge and is impacted by a cut-off mid- to upper-level low
farther north. Once Kenneth becomes a post-tropical cyclone in
about 4 days, its forward speed should slow as it reaches a weaker
steering flow. The official track forecast is nearly unchanged
through day 2 and is farther north beyond that time, based upon the
HFIP Corrected Consensus Approach.
Hurricane Kenneth Discussion Number 9
NWS National Hurricane Center Miami FL EP132017
800 AM PDT Sun Aug 20 2017
Kenneth is gradually strengthening. Satellite images show that the
cloud pattern consists of a central dense overcast and curved bands
beyond that feature, especially to the south of the center. The
Dvorak classifications from TAFB and SAB were both 4.0/65 kt, and
recent ADT values from CIMSS at the University of Wisconsin are
about the same. Based on these data, the initial intensity is
increased a little to 65 kt, making Kenneth a category 1 hurricane.
The initial motion of the hurricane is the same as before, 280/13
kt. A turn to the northwest with a decrease in forward speed is
expected to occur on Monday as a mid-level ridge to the northeast of
the system weakens. After that time, Kenneth is expected to move
even slower to the north-northwest when it moves into a break in the
ridge caused by a cut-off low near the southwestern United States.
Overall the models are in fair agreement with this scenario, but
they differ in where and when Kenneth begins to recurve. The
consensus aids have been quite consistent over the past few cycles,
and this forecast is largely just an update of the previous one.
The environmental conditions are conducive for Kenneth to strengthen
some more during the next 24 to 36 hours. After that time,
however, cooler waters along the expected track and drier air
should end the strengthening trend and cause weakening. In
addition, the global models show a significant increase in
southerly shear beginning in about 72 hours, which should aid in
the weakening trend. The intensity models are in very good
agreement, and little change was made to the previous forecast.
Kenneth will likely become a post-tropical cyclone in 4 to 5 days
when it will be over SSTs of about 23 deg C.
Tropical Storm Kenneth Discussion Number 3
NWS National Hurricane Center Miami FL EP132017
800 PM PDT Fri Aug 18 2017
Conventional satellite imagery and an earlier SSMI/S overpass show
that the depression has been strengthening during the past several
hours. Impressive outer curved banding has developed in the eastern
and northern portions of the cyclone, and the last few visible
images are showing early signs of a small central dense overcast, or
inner core formation. Based on the overall improvement of the cloud
pattern and Dvorak satellite intensity estimates of 35 kt from
SAB and TAFB, the depression is upgraded to Tropical Storm Kenneth.
The northeasterly shear is diminishing, the oceanic temperatures are
warm, and the low to mid levels of the atmosphere are moist, all
bolstering further strengthening through the 48-hour period.
Afterward, decreasing sea surface temperatures and an intruding
stable air mass from the north should result in gradual weakening.
No significant changes were made to the previous intensity forecast,
and the NHC forecast is based primarily on the IVCN multi-model
consensus.
The initial motion is estimated to be westward, or 280/13 kt.
Kenneth is embedded in the easterly mid-level flow of a subtropical
ridge extending over the eastern Pacific from northern Mexico. The
cyclone should commence a gradual turn toward the west-northwest
around the 24-hour period as a mid- to upper-level low located
just southwest of the southern California coast amplifies and
erodes the ridge to the northwest of Kenneth. Kenneth's motion is
expected to be further influenced by this growing weakness in the
ridge by decreasing in forward speed, turning northwestward on
day 3, and then north-northwestward around the 96-hour period. The
guidance suite is surprisingly tightly clustered through the entire
forecast period. The NHC track forecast is similar to the previous
one, and is hedged toward the HCCA corrected consensus model.
Tropical Depression Thirteen-E Discussion Number 1
NWS National Hurricane Center Miami FL EP132017
800 AM PDT Fri Aug 18 2017
Deep convection associated with the disturbance located over the
open eastern Pacific Ocean has become better organized early this
morning, and a primary convective band now wraps around the western
half of the circulation. Shortwave-IR and first-light visible
imagery suggest that a complex, but closed surface circulation
exists. NHC is therefore initiating advisories on Tropical
Depression Thirteen-E.
The initial intensity is set at 30 kt, in agreement with the max
winds measured in an earlier ASCAT pass and the latest Dvorak
classification from TAFB. Light easterly vertical wind shear has
thus far limited convection to the western half of the circulation,
but the GFS and ECMWF agree that the shear will lessen as the system
moves farther west. Overall, the environment appears conducive for
intensification for the next 3 days or so, and the NHC forecast
indicates that the cyclone will become a hurricane by the end of
this weekend. After that time, the cyclone will begin to weaken
over much cooler waters. The NHC forecast is very close to the
multi-model consensus, IVCN.
Since the center has only recently formed, the initial motion
estimate is a fairly uncertain 285/13 kt. There is fairly good
agreement among the global models that the tropical cyclone will
move generally westward to west-northwestward for the next 72 h
along the southern boundary of a mid-level ridge that extends
westward well into the eastern Pacific basin. A weakness in the
ridge is forecast to develop in about 3 days that should cause
the cyclone to slow and turn more toward the northwest and
eventually toward the north-northwest. The official forecast is
close to a blend of the GFS and ECMWF models.
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