Also see this excerpt from a dailykos diary written by a blogger who indicated that he has studied meteorology: Rita: The Next Few Hours Are Critical [by Todd Johnston Tue Sep 20th, 2005]
"A hurricane's central pressure (CP) is a simple and very effective measure of its strength. Over at the ePluribus Media Community site I'm keeping a running table of Rita's CP, from each 3-hr NWS advisories going back to last night. If you'd like to see the progression, follow the link above.
Starting with the 8:00 a.m. NWS advisory, Rita's CP began decreasing rapidly -- about 1-2 millibars/hour. The difference between a weak hurricane and a strong one is only about 50 millibars, so 1-2 millibars/hour for any length of time spells trouble.
Katrina briefly made landfall in Florida, weakening her quite a bit. But she made it through to the warm waters of the Gulf of Mexico where she stalled and gained strength.
Rita, however is a 'small' storm in the sense that hurricane force winds only extend outward from her eye about 50 miles. That's roughly 1/3 the size of Katrina. While that is usually good news, it's allowed Rita to slip right in-between Florida and Cuba. She is now southwest of the keys and moving west, and while many hurricanes lose strength during this passage, Rita's central pressure dropped from 978 to 973 mb between 2:00 and 5:00 p.m.
The fact that she is not a big storm may be the best news of all, however the GOM has been warmer than normal for the last 6 weeks. Hurricanes feed off warm surface waters -- that is why what happens next is so important.
If Rita stalls and sits around in the GOM, she will likely strengthen. Over the next few hours watch for 2 things in particular:
Keep track of Rita's CP. If it continues to drop, or stays the same and then drops suddenly, that spells trouble.
See if Rita slows and hangs around the Gulf before making landfall. That will give her time to strengthen.
Hopefully, neither of these will happen. If Rita's central pressure levels out and she keeps moving, she'll probably end up making landfall near eastern Texas as a weak Cat 2 or Cat 1."