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Subtropical Storm ANA (Text)


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Subtropical Storm Ana Discussion Number   4
NWS National Hurricane Center Miami FL       AL012021
1100 PM AST Sat May 22 2021

Ana continues to produce a small, but concentrated area of moderate 
convection near its center. The storm remains embedded in a 
large-scale upper-level trough axis, and convection near the center 
has not been deep or expansive enough to result in significant 
upper-level anticyclonic outflow. This structure suggests that the 
system remains subtropical. However, scatterometer imagery also 
indicates that Ana's radius of maximum winds is very small. A recent 
METOP-B ASCAT pass at 0054 UTC had a peak wind retrieval of 36 kt 
just southeast of Ana's center. Due to the small size of Ana's wind 
field and allowing for some undersampling of this instrument, the 
initial intensity was bumped up to 40 kt for this advisory.

Ana has begun to accelerate to the northeast and its initial motion 
is now 050/8 kt. A continued northeastward motion at an increasing 
forward speed is expected as deep-layer southwesterly steering flow 
increases between a deepening mid-latitude trough to the northwest 
and a subtropical high to the southeast.

The upper-level trough axis that Ana remains centered in has kept 
the tiny cyclone in a small region of light upper-level flow, 
allowing convection to persist near the center. However, as Ana 
accelerates northeastward, this trough axis will gradually decay and 
upper-level northerly flow is expected to increase after 12 h. The 
resulting increase in northeasterly shear will import dry 
mid-latitude air and likely strip away the remaining convection 
associated with Ana by tomorrow night. The latest intensity forecast 
calls for slow weakening after 12 h with dissipation by 48 h, though 
it is possible that Ana could dissipate earlier than currently 
forecast.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/0300Z 35.0N  61.4W   40 KT  45 MPH
 12H  23/1200Z 35.8N  60.0W   40 KT  45 MPH
 24H  24/0000Z 37.5N  56.3W   35 KT  40 MPH
 36H  24/1200Z 41.1N  50.5W   35 KT  40 MPH
 48H  25/0000Z...DISSIPATED
 
$$
Forecaster Papin/Brown
 
NNNN

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Page last modified: Friday, 15-Oct-2021 12:09:05 UTC