2012 Atlantic Hurricane Season Birdseye Discussion #7A (Special Update)
...APRIL 19 2012...
This partial discussion is issued as a special update concerning special feature Invest 91-L mentioned in previous full discussion #7.
The parent upper low over 91-L has been shifting northward througout the day as it becomes increasingly gravitated toward a central US upper trough approaching from the west. The surface low of 91-L began tracking eastward last evening while steered by the south side of the upper low and was expected to soon turn northward while entering the east side of the upper low. The northward turn of the surface low will now be delayed due to the northward shift of the parent upper low. This is because the surface low will be embedded in vast steering westerlies south of the upper low. The prolonging of the surface low's eastward track give its more time before it will be absorbed by the cold front of the incoming central US upper trough.
Despite more time till absorption...Invest 91-L is no longer a risk of subtropical cyclone formation as the surface low of Invest 91-L no longer has bursts of convection. The loss of convection perhaps is also attributed to the northward shift of the parent upper low. The coldest temps of the upper low center have moved away from the surface low as the upper low shifted northward. This upper-level cold air was crucial in de-stabilizing the atmosphere of the surface low...which is tracking over mild water temps of 20 to 21 deg C and needs upper-level cold air to produce convection at those water temps. The loss of convection may also be attributed to dry air ingestion of neighboring dry air S of Bermuda mentioned in discussion #7.
With 91-L not expected to develop into a subtropical cyclone, this is the last birdseye Atlantic discussion until Atlantic Hurricane Season starts June 1 2012.