14 September 2006

Gordon strengthens, Helene forms...

At 03Z last night, Gordon was upgraded to 105kts, making it the first major hurricane of the season (CAT3+).  Twelve hours later, it's maintaining that 105kt intensity, with an MSLP of 955mb.  Just 24 hours ago, it was 80kts and 977mb, then 48 hours ago it was 50kts and 1000mb.  This didn't touch any rapid intensification records, but was still impressive.

The satellite presentation is spectacular: a large 40-mile-wide clear eye, symmetric convection, and few spiral rainbands.  However, things are about to change... looping the recent satellite imagery reveals an insurgence of westerly vertical wind shear, which will eventually reach a critical level and disrupt Gordon's major hurricane lifestyle.  Typically, once the shear is >20kts, the vertical coherence of the vortex is upset, and this is forecast to occur within the next 12 hours.  In about two days, it could already be weakened to a tropical storm.

It's forecast to maintain its current intensity for the next 6-12 hours, then gradually start weakening as it heads NNE-NE into cooler water and higher shear.

TD8 was upgraded to TS Helene, the 8th named storm of the season, at 03Z last night.  Although it's a VERY broad and diffuse surface circulation, the estimated intensity is 40kts and 1003mb.

It is predicted to remain over warm water with low to moderate shear, which should allow it to achieve an intensity similar to Gordon's within 4-5 days.  Again, the majority of models turn the storm more NW in 3-5 days, as the weakness in the subtropical ridge allows it to slip up that way (the same one responsible for steering Gordon into the north central Atlantic).

For those who keep tabs on the season's Net Tropical Cyclone Activity (NTC), 2006 is at 50.2% as of 15Z this morning, with the largest contribution coming from Gordon at 16.5%.  For comparison, we were at nearly 150% last year at this date.

Please visit my tropical Atlantic headquarters.

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