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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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