Irene Becomes Tropical Storm Again ... Threat to Carolinas Decreasing

What has changed since last night, overall? Not a whole lot, really, but enough to make mention.

The upper-low noted east of the Bahamas yesterday is still there, though it is slowly moving west and showing signs of narrowing. However, this is where the weakness is right now and what is likely sending Irene on a 300deg path. If Irene keeps going at this path, it may well round through the weakness in the ridge pretty slowly and ultimately head out to sea. Not a strong possibility, but there nonetheless. The satellite data suggest this is possible moreso than the actual height data -- the ridge north of Irene is narrow and, per the steering flow data available at the UWisconsin site, is weak enough to allow for something to slide through. As a result, I wouldn't be so quick to discount the NOGAPS/UKMET solutions just yet.

However, as this feature moves west, the storm should start to veer back to the west-northwest. Other than this feature, the tendency would be for Irene to move closer to 285deg. I expect a general 290deg motion to resume tomorrow, assuming the upper low continues to move away/fill. The next weakness lies directly along the coast, stretching from the Outer Banks across the northern parts of Ga/Al/Ms, but does not appear to be moving any further southward. A number of weak upper-level lows have formed along this boundary back to the west, with a persistent TUTT cell in the northern Gulf of Mexico. I don't expect a lot of motion from these features, but their building will help to amplify the pattern just slightly. Whether this means a tendency to send the storm more towards the west or more towards the north remains to be seen...right now, either possibility is about equally likely. The flow remains zonal across the eastern 2/3 of the US -- a shortwave trough is passing just to the north of Irene right now and may have also played a role in the jog northward today -- and with nothing down the line to suggest this will change, it is going to be fluctuations in the intensity and position of the subtropical ridge and boundary draped across the SE US that determine where this storm ultimately goes. Georgia is looking less likely with time as well, and the all-clear can about be sounded for a direct impact to Florida, but folks from Savannah northward really need to keep an eye on this one.

The low-level center and mid-level center are not aligned very well this evening -- another reason why you don't use infrared satellite imagery as the sole marker of a storm's intensity -- with the former moving ~300deg and the other building closer to ~315deg with the morphing of the convective pattern. As a result, I don't expect any change in intensity once again at 11pm. Once -- if -- the two become better aligned, some modest intensification is possible and likely. It is relatively dry in the vicinity of the storm, but not as much as before. Shear is still present, but the transverse banding features (e.g. outflow pattern) are getting better defined, especially to the north and east, with time. The GFS solution is possible, given the current state of organization, but not likely at this point.

More tomorrow, if needed...we'll get the first recon fixes in time for the 5p advisory package tomorrow afternoon.

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