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Subtropical Storm Ana Forecast Discussion Number 4
2021-05-23 04:51:20| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sat May 22 2021 000 WTNT41 KNHC 230251 TCDAT1 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
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