Tropical Storm Ana – NWS National Hurricane Center Miami FL 1100 PM AST Sat May 22, 2021 (see video below)
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 the current forecast.
FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 38.3N 55.2W 35 KT 40 MPH - Post Tropical (ENE St Georges, Bermuda) 12H 24/1200Z 41.0N 50.5W 30 KT 35 MPH - Low (ENE St Georges, Bermuda) 24H 25/0000Z...DISSIPATED
NWS National Hurricane Center Miami FL 1100 AM AST Sat May 22, 2021
Satellite imagery and radar data from Bermuda indicate that the central convection associated with Ana has changed little in organization during the past several hours, with a complex of small bands near the center at this time. The initial intensity will be held at 40 kt based on the latest intensity estimate from TAFB, although recently-received ASCAT data suggests this could be a little generous. Although the cyclone has some characteristics of a tropical cyclone, Ana remains a subtropical storm based on its position near the center of a large upper-level low-pressure system and the current lack of anticyclonic upper-level outflow.
The initial motion is 270/3. Ana and the large low it is embedded in are expected to turn northward later today as a developing mid-latitude cyclone over eastern Canada and the New England states erodes the subtropical ridge west of Ana. After that, the storm is expected to turn northeastward on the southeast side of the mid-latitude cyclone. The track guidance is in good agreement with this scenario, and the new track forecast is similar to, but a little slower than, the various consensus models.
Little change in strength is expected for the next 12 h or so. After Ana recurves, a combination of increasing shear, dry air, and decreasing SSTs should cause the storm to gradually weaken tonight and Sunday. The large-scale models agree upon Ana opening up into a trough of low pressure in 36-48 h, and the official forecast shows this happening just after 48 h. The remnant trough will likely be absorbed by a cold front associated with the mid-latitude cyclone shortly thereafter.
The Bermuda Weather Service has discontinued the Tropical Storm Watch for Bermuda.
FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 34.3N 63.0W 40 KT 45 MPH - Post Tropical (ENE St Georges, Bermuda) 12H 23/0000Z 34.8N 62.8W 40 KT 45 MPH - Post Tropical (ENE St Georges, Bermuda) 24H 23/1200Z 35.8N 61.2W 35 KT 40 MPH - Post Tropical (ENE St Georges, Bermuda) 36H 24/0000Z 37.2N 57.9W 35 KT 40 MPH - Post Tropical (ENE St Georges, Bermuda) 48H 24/1200Z 39.7N 52.9W 35 KT 40 MPH - Post Tropical (ENE St Georges, Bermuda) 60H 25/0000Z...DISSIPATED
Video: Subtropical storm Ana becomes first named storm of 2021 hurricane season