2 Oct Tue 2018

LESLIE STRENGTHENS SLIGHTLY WHILE MOVING SLOWLY SOUTHWESTWARD OVER THE CENTRAL ATLANTIC

Tropical Storm Leslie Discussion Number 24
NWS National Hurricane Center Miami FL AL132018
500 AM AST Tue Oct 02 2018

Infrared and passive microwave satellite imagery indicate that
convection has increased and become better organized around the
well-defined low-level circulation center. In fact, recent
microwave images showed that Leslie has developed a closed, 20- to
25-nmi wide low-level eye. Based on the presence of the distinct
low-level eye feature and a Dvorak intensity estimate of T3.5/55 kt
from SAB, the cyclone’s intensity has been increased to 55 kt.

The initial motion is southwestward or 220 degrees at a faster
forward speed of 6 kt. For the next 24 h or so, Leslie is forecast
to move slowly southwestward to south-southwestward, trapped between
a deep-layer ridge to the west and a mid- to upper-level low to the
east. After possibly becoming stationary near the 36-h period, a
ridge to the southeast and east of Leslie is forecast to become
highly amplified, forcing the cyclone northward into the higher
latitudes through 72 h. On days 4 and 5, an approaching mid-latitude
shortwave trough well to the north of Leslie is forecast to nudge
the cyclone eastward, but only slowly at forward speeds of less than
10 kt. The new NHC forecast track has again been adjusted to the
left of the previous advisory track in the 36- to 72-h period, and
is similar to but slightly east of the various consensus models.

Leslie’s outflow pattern has become a little more symmetrical during
the past 6 h, and further improvement is expected through 72 hours.
In addition, lightning data and satellite imagery during the past
few hours indicate that convection has been developing in the dry
slot to the north and east of the main convective band, suggesting
the mid-level environment is finally beginning to moisten. This dry
intrusion has been hindering the development of deep eyewall
convection and, thus, the lack of intensification of the cyclone.
However, given the strong instability that is forecast to develop in
the inner-core region region due to very cold air aloft moving over
relatively warm waters of near 26C beneath the cyclone, along with
increasing outflow and mid-level moisture, slow but steady
strengthening seems reasonable for the next 48 hours or so. By 72 h
and beyond, gradual weakening is expected as Leslie moves back over
cooler oceanic temperatures and dry mid-level air from the
mid-latitudes associated with the aforementioned shortwave trough
once again gets entrained into the cyclone’s circulation. The
official intensity forecast is just an update of the previous
advisory, and is similar to the weaker IVCN consensus model.

Large swells generated by Leslie will continue to affect portions of
the southeastern coast of the United States, Bermuda, and the
Bahamas. These swells could cause life-threatening surf and
rip currents. Although the swells are forecast to abate temporarily
in the Bahamas later today, they are expected to increase again on
Wednesday and Thursday, and propagate farther southward into the
Greater and Lesser Antilles. Please consult products from your
local weather office.

FORECAST POSITIONS AND MAX WINDS

INIT 02/0900Z 31.6N 55.6W 55 KT 65 MPH
12H 02/1800Z 30.6N 56.1W 60 KT 70 MPH
24H 03/0600Z 29.9N 56.5W 65 KT 75 MPH
36H 03/1800Z 30.2N 56.6W 70 KT 80 MPH
48H 04/0600Z 31.3N 56.4W 70 KT 80 MPH
72H 05/0600Z 35.0N 56.3W 65 KT 75 MPH
96H 06/0600Z 37.1N 54.8W 60 KT 70 MPH
120H 07/0600Z 37.1N 51.9W 55 KT 65 MPH

$$
Forecaster Stewart