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By: NCHurricane2009 , 5:46 PM GMT on May 19, 2012
...MAY 19 2012...
This partial discussion is issued as a special update concerning the special feature off of the Carolina coast mentioned in full discussion #12. This special feature appears to be forming into a tropical storm...and I am forecasting a 100% chance that it will do so. In lieu of this forecast...I am waiting to write the next full birdseye discussion when the National Hurricane Center upgrades this to a tropical storm. If it is not upgraded...I will be writing the next full birdseye discussion late this evening.
See full discussion #12 for how this disturbance off of the Carolinas originated. Figure 1 below serves as an update to Figure 1 from discussion #12. The system has rid itself of the two unfavorable conditions mentioned in the previous discussion...warding off the dry air in its SE half by firing persistent heavy T-storms near the center...and having the SW LLC (low-level circulation) tighten up and consolidate so that it is now seperate from the northeastern LLC. Its current structure and favorable conditions (anticyclonic outflow to its north shown in Figure 1 and warm Gulf stream waters) suggest an imminent chance it will become a tropical storm...and so this is what I am predicting at this time (1:46 PM EDT). The National Hurricane Center put the odds at 50% late this morning...and the Navy NRL upgraded the system to Invest 93L.
Radar from Wilmington, North Carolina (Figure 2 below) suggests the southwestern LLC (Invest 93L) is moving slowly toward the west at the moment. It also suggests a very small tropical storm developing with the compact spiral rain shield entirely offshore. There is also deep-layered cyclonic flow towards the northeast with the NE LLC evolving into a mature extratropical (non-tropical) low. And finally...previous discussion #12 mentioned the system was "hugged by low-level ridging to its west...north...and east." With all this initial information...where will the system go and what impacts will it give?
I forecast the current slow west and southwest motion to continue while influenced by the deep-layered LLC to the northeast and low-level ridging to the northwest. This will keep the compact rain shield offshore and limit coastal impacts (Carolinas...Georgia...and N Florida) under some increased surf but more importantly rip currents. Once the northeastern LLC accelerates away to the NE...I expect the storm to stall and meander erratically like a pinball inside a pinball machine...bouncing between the low-level riging surrounding the system to the west...north...and east. Then late on May 21...I expect an acceleration towards the NNE as the next frontal system from the western US erodes the ridging to the NW. Exactly where the center is after its erratic motion depends on the coastal impacts during its NNE acceleration. Given its compact sturcture...a more offshore NNE track will continue to limit impacts to surf and rip currents. A NNE track closer to shore will add heavy rainfall and gusty northerly winds to the list of impacts. Interests along the Carolina and New England coasts should monitor this system carefully through the weekend into early next work week.
Figure 1: Updated view of coastal Carolina storm's structure. This is updated from last night's Figure 1 in discussion #12
Figure 2: Radar image of organizing storm off of the Carolina coast. Note the well-defined LLC (low-level circulation) at the center of spiral rain bands.
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