04 September 2008

Hanna heading northwest, Ike rapidly intensifies, Josephine getting sheared...

Hanna is succumbing to strong vertical shear and very dry ambient air, and is now not much more than a broad exposed low-level circulation.  It still has some convection associated with it, but it's weak and far removed from the center.  It's still being classified as a 55kt tropical storm, and forecast to reach minimal hurricane status before landfall on Saturday morning near the central NC coast (despite no model guidance supporting that intensity).  It is now located just north of the central Bahamas and tracking NW.

When I wrote my update yesterday, Ike was a 60kt tropical storm with a central pressure of 991mb.  Six hours later, it was at 70kts and 984mb.  Another six hours: 115kts and 948mb.  And yet another six hours: 125kts and 935mb.  So, the pressure fell 36mb in 6 hours, 49mb in 12 hours, and 61mb in 24 hours.  Ike very easily met the criteria for rapid intensification, and also was within 5-10kts of its Maximum Potential Intensity (MPI).  MPI is a theoretical upper bound for a storm's intensity given its location, oceanic and atmospheric environments, etc.  Few storms reach their MPI, and some even exceed it (because MPI is not a flawless quantity).

Here are infrared and microwave satellite images from 0745Z and 1136Z today, with Ike as a 125kt hurricane:

So, Ike reached a peak intensity (so far) at 09Z today, at 125kts and 935mb.  As of the 15Z advisory, it's 120kts and 938mb, still a powerful Category 4 storm.  It is starting to encounter some moderate northerly vertical wind shear, and should continue to gradually weaken over the coming 2-3 days (still a strong hurricane though), then after 3 days, the shear is expected to let up a bit, allowing Ike to reintensify as it heads into the Bahamas early next week.  It's presently located near 23N 58W and moving WNW at 14kts.

Josephine is in a hostile environment and barely holding steady as a 45kt tropical storm.  Like Hanna, its satellite presentation is poor, at best.  It will be in strong shear for the next 4 or so days, then perhaps have a shot at regeneration.  In the meantime, it will track WNW over open ocean... not a threat to any land or island for at least a week.

Please visit my tropical Atlantic headquarters.

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