Post-Tropical Cyclone Flossie Discussion Number 35
NWS Central Pacific Hurricane Center Honolulu HI EP072019
500 PM HST Mon Aug 05 2019
Vigorous deep convection has been persistent through much of the day
to the northeast of the cloud system center, which has become
significantly elongated and poorly defined by several outflow
boundaries. Recent analyses of satellite cloud drift winds suggest
that the highly elongated cloud system center is lacking westerly
winds that define a closed area of low pressure, and subjective
Dvorak current intensity estimates were 25 kt from HFO and SAB,
while JTWC deemed the system too weak to classify. Given these
inputs and the presence of continued vertical wind shear of more
than 30 kt, Flossie will be designated a post-tropical remnant low.
The intensity will remain 30 kt, since an ASCAT-C pass earlier in
the day detected winds this strong within the deep convection. While
the cloud system center could arguably be a trough, a mean center
location gives an initial motion of 300/10 kt.
Under relentless vertical wind shear, the remnant low will continue
to degenerate as it passes near the main Hawaiian Islands. The
westerly vertical wind shear will be maintained by a deep
upper-level trough parked northwest of the Hawaiian Islands. This
upper trough is also eroding the low- to mid-level ridge that is
steering Flossie. As a result, the remnant low will gradually turn
toward the northwest tonight, then shift toward the north-northwest
until dissipation on Wednesday. The track forecast was nudged to the
right from the prior advisory and is near TVCN. All guidance shows
weakening or little change in intensity until dissipation.
This is the last advisory on Flossie. Additional information on this
system can be found in the High Seas Forecasts issued by the
National Weather Service in Honolulu under AWIPS header HFOHSFNP and
WMO header FZPN40 PHFO. Interests in the main Hawaiian Islands
should refer to products issued by the National Weather Service in
Honolulu for information on flooding and surf impacts.
Tropical Storm Flossie Discussion Number 23
NWS Central Pacific Hurricane Center Honolulu HI EP072019
500 PM HST Fri Aug 02 2019
Tropical Storm Flossie has crossed into the Central North Pacific
basin as a messy system. Satellite images indicated limited deep
convection displaced northeast of the partially exposed low level
circulation center. Dvorak intensity estimates came in at 3.0/45 kt
from PFHO, JTWC, and SAB, and the CIMSS ADT value at 3/0000 UTC was
3.3/51 kt. Based on a blend of these estimates, and the poor
appearance in satellite imagery, the initial intensity for this
advisory has been lowered to 50 kt.
There is no change to the forecast track plan. Flossie continues to
move west-northwestward under the influence of a subtropical ridge
to the north of the cyclone. This direction of motion is expected to
continue over the next 48 hours but with a slightly slower forward
speed. Large-scale models indicate that the ridge will weaken as an
upper level trough approaches from the northwest. This should turn
Flossie toward a northwestward, and then northward track beyond the
48 hour time frame. All of the models are in general agreement with
this scenario, though HWRF and HMON indicate less of a turn and are
thus on the southern side of the guidance envelope. The forecast for
this advisory is right on the previous forecast through 24 hours,
then nudged slightly south of the previous track from 36 hours and
beyond to line up more closely with the TVCN and HCCA consensus.
Flossie is expected to traverse over marginal sea surface
temperatures through the forecast period. Furthermore, vertical
shear is expected to increase to above 30 knots after 48 hours in
the ECMWF SHIPS guidance. Given these factors, the model intensity
guidance shows continued weakening through the forecast period. The
current forecast is close to the IVCN and HCCA guidance, and makes
Flossie a tropical depression after 48 hours to the east of the main
Hawaiian Islands.
Tropical Depression Seven-E Discussion Number 1
NWS National Hurricane Center Miami FL EP072019
900 AM MDT Sun Jul 28 2019
First-light visible satellite images have revealed that the area of
low pressure located southwest of the coast of Mexico has developed
a well-defined center of circulation. The convective pattern has
also increased in organization, with a pronounced band wrapping from
the west to north of the center. Dvorak intensity estimates are
T2.0/30 kt from SAB and T1.5/25 kt from TAFB, and advisories are
being initiated on a 30-kt tropical depression.
Tropical Depression Seven-E is moving quickly along the southern
periphery of mid-level ridging that is centered along the U.S/Mexico
border, and its initial motion estimate is 285/18 kt. A weakness in
the ridge west of the Baja California peninsula should allow the
cyclone to slow down some after 24 hours, but the trajectory is
expected to be either westward or west-northwestward for the entire
5-day forecast period. There is very little spread among the track
models, and this initial NHC forecast has generally been placed
between the various multi-model consensus models and the HFIP
Corrected Consensus aid (HCCA).
The convective pattern and upper-level cloud motions suggest that
there's a little bit of shear over the system from the
east-northeast, but that shear should abate over the next 24 hours.
The cyclone will also be over deep warm water, with sea surface
temperatures remaining above 27 degrees Celsius for the entire
forecast period. As a result, steady strengthening is anticipated,
and the NHC intensity forecast is slightly above the IVCN intensity
consensus and close to the HCCA guidance for much of the forecast
period. The depression is forecast to become a tropical storm later
today, and it is likely to become a hurricane in 2 to 3 days.
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