TROPICAL STORM RICK DISCUSSION NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL EP212015
900 AM CST THU NOV 19 2015
The cloud pattern of the cyclone is better organized than this time
yesterday. First-light visible imagery indicates that the low-level
center is underneath a circular mass of deep convection, and there
has been an increase in banding features and their associated
curvature. The increase in organization could be a sign of some
decrease of the southeasterly shear that has been affecting the
cyclone. A Dvorak intensity estimate of T2.5 from TAFB and an
UW-CIMSS ADT value of 2.9 is used to raise the initial intensity
estimate to 35 kt.
Some further decrease in southeasterly shear is likely through
early Friday. With large-scale environmental conditions otherwise
largely favorable, intensification is shown through about 24 to 36
hours. The window of opportunity for strengthening should be short-
lived though, since west-southwesterly shear is forecast to increase
by 48 hours when Rick moves north of the upper-level ridge axis.
The shear should become prohibitively high by 72 hours ahead of a
shortwave trough in the eastern Pacific subtropics being ejected
eastward toward the cyclone. The result should be rapid weakening,
and remnant low status is likely by 96 hours, if not sooner.
Dissipation is now shown by 120 hours. The new NHC intensity
forecast is slightly above the previous one, and shows and earlier
peak, with remnant low status indicated sooner.
The center has been difficult to locate but seems to be slightly
farther east than previous estimates based on a couple of microwave
passes and visible imagery. The best estimate of the initial motion
is north or 360/06. Global models show mid-level ridging building to
the north of the cyclone today, and the depression should be respond
by moving more quickly toward the northwest and then west-northwest
over the next day or two. Rick should reach the western periphery
of this ridge in 3 to 4 days and begin to move more poleward, but
will likely dissipate before responding to the trough in the
subtropics moving toward it. The new track forecast is right of the
previous one, primarily due to the more eastward initial position
estimate.
Only 3 tropical storms have formed later than this calendar date in
the eastern North Pacific since reliable records began in the early
1970s.
TROPICAL DEPRESSION TWENTY-ONE-E SPECIAL DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL EP212015
1000 AM MDT WED NOV 18 2015
The circulation associated with the low pressure system located
several hundred miles south-southeast of the southern tip of Baja
California has become well-defined overnight according to
scatterometer data. These data and first-light visible satellite
imagery also indicate the that center of the cyclone is near the
southeastern edge of large mass of cold-topped convection,
suggesting the presence of some southeasterly shear. A Dvorak
classification of T2.0 from TAFB, along with the earlier
scatterometer data, is used to set the intensity to 30 kt.
Since the history of fixes on this system is short, the initial
motion estimate of 360/02 is somewhat uncertain. A deep trough over
the central United States has created a significant weakness along
110W, which has made for a weak steering environment around the
depression. However, a weak mid-level anticyclone to the south of
mainland Mexico has been imparting a slow northward motion. This
motion should continue for another 24 hours, at which time a
mid-level ridge over the Gulf of Mexico is forecast to build
westward into the eastern Pacific when the central U.S. trough lifts
out. The building ridge should result in a northwestward and then a
west-northwestward track through 72 hours. After that time, a
trough currently between 130W and 140W in the subtropics is forecast
to eject eastward toward the cyclone and result in its recurvature
in about 96 hours. The official forecast track is on the left side
of the guidance envelope, closest to the ECMWF and GFS solutions,
and generally near the multi-model consensus.
There are mixed signals on the potential for intensification in the
short term. Although the waters are anomalously warm, some
southeasterly shear is likely to continue to affect the cyclone over
the next day or two, along with some drying of the lower to middle
troposphere. These large-scale conditions suggest that some
strengthening should occur, but it likely would be tempered by these
two negative factors. Around 72 hours, the cyclone should encounter
an environment of increasing south-southwesterly or southwesterly
shear associated with the trough advancing from the west and rapidly
weaken, likely becoming a remnant low by day 5, if not sooner. The
official intensity forecast is a little above the multi-model
consensus and closest to the ECMWF SHIPS output.
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