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Tropical Storm Marie Discussion Number 5
NWS National Hurricane Center Miami FL EP182020
300 AM MDT Wed Sep 30 2020
Geostationary satellite imagery shows that Marie continues to
become better organized with a curved band of convection over the
western semicircle and a small central dense overcast feature. An
ASCAT-B overpass from around 0515 UTC was very helpful in
pinpointing the center, and it also revealed that Marie's
tropical-storm-force wind field is quite small. Subjective
satellite intensity estimates of T3.0 and the scatterometer
data yielded an intensity of 45 kt at 0600 UTC, but given the
continued improvement in organization, the advisory intensity
has been set at 50 kt.
Although Marie's outflow is somewhat restricted over the
northeastern portion of the storm due to some northeasterly shear,
it has been expanding over the past few hours indicating that the
shear is decreasing as anticipated. Marie is forecast to remain
over warm waters and in a low shear environment during the next
couple of days. These very conducive conditions favor
strengthening, and the NHC intensity forecast calls for steady to
rapid intensification over the next 48 hours. The official
forecast is in good agreement with the SHIPS, LGEM, and HFIP
corrected consensus models which all predict periods of rapid
strengthening over the next 48 to 60 hours. The updated NHC wind
speed forecast shows a faster rate of strengthening and a slightly
higher peak intensity than in the previous advisory. After 72
hours, cooler waters and a more stable environment should result in
steady to rapid weakening.
Maria is moving westward at about 14 kt, a little faster than
before. There has been no change to the track forecast philosophy
as Marie is expected to move westward to west-northwestward during
the next few days while it remains to the south of a deep-layer
ridge. After that time, a slower northwestward motion is predicted
when Marie approaches a weakness in the ridge. The latest runs of
the dynamical models have trended toward a more westward track
during the first 60 hours or so, and the official forecast has been
adjusted accordingly. Thereafter, the NHC track is fairly similar
to the previous advisory, and it again lies near the middle of the
guidance envelope.
Marie's 12-ft sea radii remain larger than would be expected for a
small tropical storm due to a large fetch of southerly swell
originating from the Southern Hemisphere.
FORECAST POSITIONS AND MAX WINDS
INIT 30/0900Z 14.1N 112.5W 50 KT 60 MPH
12H 30/1800Z 14.4N 114.8W 60 KT 70 MPH
24H 01/0600Z 14.5N 117.7W 75 KT 85 MPH
36H 01/1800Z 14.9N 120.5W 90 KT 105 MPH
48H 02/0600Z 15.7N 123.1W 105 KT 120 MPH
60H 02/1800Z 16.8N 125.3W 110 KT 125 MPH
72H 03/0600Z 18.0N 127.2W 100 KT 115 MPH
96H 04/0600Z 20.0N 130.2W 75 KT 85 MPH
120H 05/0600Z 21.5N 133.0W 55 KT 65 MPH
$$
Forecaster Brown
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