TROPICAL STORM LISA DISCUSSION NUMBER 4...CORRECTED
NWS NATIONAL HURRICANE CENTER MIAMI FL AL132016
1100 AM AST TUE SEP 20 2016
CORRECTED LISA TO BE TWELFTH NAMED STORM
The cloud pattern of the cyclone has steadily improved, with long
curved bands having developed in the northern semicircle since the
previous advisory. Although Dvorak satellite classifications from
TAFB and SAB were 30 kt at 1200Z, recent UW-CIMSS ADT values have
increased to 35 kt and AMSU intensity estimates range from 35-45 kt.
Therefore the initial intensity has been increased to 35 kt, which
is a compromise of these estimates, making the cyclone the twelfth
named storm of the 2016 hurricane season.
Visible satellite imagery indicates that Tropical Storm Lisa is now
moving northwestward or 305/10 kt. Water vapor imagery and
satellite-derived winds indicate that a large mid-latitude trough
extends from near the Canary Islands southwestward into the tropics,
which has created a break in the subtropical ridge along 30W-40W
longitude. Lisa is forecast to move generally northwestward toward
the break in the ridge for the next 4 days, followed by a northward
turn as the cyclone moves around the western periphery of the ridge
axis. The latest model guidance remains in good agreement on this
track scenario, and the new NHC forecast track is just a little to
the right of the previous advisory track, mainly to account for the
more northward initial position, and lies close to the consensus
model TVCN.
Lisa has about 48 hours remaining to strengthen while the vertical
wind shear and upper-level outflow pattern remain favorable, and
sea-surface temperatures are above 27 deg C. However, a marginally
moist mid-level environment and the large size of the cyclone are
expected to prevent any rapid strengthening from occuring. After
that time, the atmosphere is expected to become quite hostile,
characterized by southwesterly shear of 25-30 kt and much drier
mid-level air, resulting in steady weakening from 72-120 hours.
Although the dynamical guidance continues to forecast some
relaxation of the shear toward the end of the period, the cyclone
will likely be too degraded to recover. The official intensity
forecast is close to the SHIPS model through 48 hours, and then lies
closer to the LGEM guidance after that.
TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL132016
1100 PM AST MON SEP 19 2016
The coverage of deep convection associated with the depression has
decreased somewhat during the past several hours, but the
circulation remains well established with several fragmented
curved bands. Satellite intensity estimates from TAFB and SAB
support maintaining the initial wind speed of 30 kt.
The cyclone is moving west-northwestward at 8 kt. A weakness in
the subtropical ridge over the east-central Atlantic is expected to
persist for the next several days due to a series of shortwave
troughs moving through the area. As a result, a continued
west-northwestward to northwestward motion at about the same forward
speed is expected throughout the forecast period. The models are in
fair agreement, and the NHC track prediction lies on the left side
of the guidance envelope, in best agreement with the ECMWF model.
The environmental conditions for strengthening during the next
several days are mixed. Although the shear is expected to be light
and waters warm during the next couple of days, the atmosphere is
not overly moist in the vicinity of the depression. These
conditions should allow for slow strengthening during the next 48
hours. Beyond that time, however, the system is expected to move
in less favorable conditions of stronger shear, even drier air, and
more marginal SSTs. These conditions should halt strengthening
and induce gradual weakening. The NHC intensity forecast lies
close to the intensity model consensus for the first few days, but
is lower than the consensus at days 4 and 5 given the expected
hostile conditions.
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