Paula intensifies to Category 2

Hurricane Paula put on a respectable burst of intensification early this afternoon, popping an eye and reaching Category 2 strength. Last night and early this morning, Paula set a modern record for the fastest intensification from the issuance of the first advisory to hurricane strength, performing the feat in just 12 hours. At 1pm this afternoon, an Air Force hurricane hunter aircraft measured surface winds of 104 mph with their SFMR instrument in Paula's northeast eyewall. On the second pass through the eyewall at 2pm, the SFMR saw top winds of 85 mph, in Paula's northwest eyewall, and the pressure had dropped 1 mb in one hour. The aircraft passed through the northeast eyewall again near 3pm EDT, and found weaker surface winds, just 83 mph, compared to the 104 mph seen at 1pm. The pressure remained the same as at 2pm, suggesting that Paula is done intensifying. Paula is a small hurricane, with hurricane force winds that extend out just 10 miles from the center. The eye is very tight, with a diameter of 11 miles. The Hurricane Hunters noted something in their comments I've never seen before--the eye was more square than circular.


Figure 1. Radar image at 3pm EDT 10/12/10 from Cancun, Mexico, showing rain from an outer spiral band over Cozumel Island, and the core of Paula to the south-southeast of the island. Image credit: CONAGUA Mexico.

Satellite imagery has been showing the intermittent appearance of an eye this afternoon, and Paula has been growing more organized, with improving low-level spiral banding and upper-level outflow. Water vapor satellite loops indicate that the atmosphere in the Western Caribbean is moist enough to support further development, but moderate wind shear of 15 - 20 knots, due to strong upper-level winds out of the south, is slowing Paula's intensification.


Figure 2. Rain rate (inches per hour) as measured by the TRMM satellite at 12:29 pm EDT 10/12/10. Peak rain rates of 0.8 inches/hr (yellow colors) were occurring in a spiral band on Paula's west side. Lower rain rates of 0.6 inches/hr (green colors) were seen in the eyewall. Image credit: Navy Research Lab, Monterey.

Forecast for Paula
Radar from Cancun shows that an outer spiral band moved over Cozumel between 2 - 3pm EDT, bringing a brief heavy rain squall to the island. This band will move inland over the Yucatan Peninsula, bringing a brief heavy rain squall to Cancun late this afternoon. Radar and satellite imagery indicate about a six-hour break after passage of this spiral band before the next major band hits, late tonight. Tropical storm force winds of 39+ mph extend out from Paula's center about 70 miles to the north. Paula's current north-northwest motion of 10 mph means that tropical storm force winds should reach the coast of Mexico near Cozumel between 8pm - 2am local time tonight. A good way to visualize this is to use our wundermap with the "hurricane" layer turned on, and click on the "forecast" and "wind radius" boxes. Hurricane force winds extend out just ten miles from the center, so only a very small region of coast will receive Paula's strongest winds. The 1:45pm EDT wind probability product from NHC gives a 99% chance that Cozumel will receive tropical storm force winds, and a 60% chance of getting hurricane force winds of 74+ mph. In addition to high winds, heavy rain will be a major threat. If Paula stalls as expected and wanders in the region for many days, rainfall forecasts from the HWRF and GFDL models suggest that Paula will be capable of dumping more than a foot of rain in isolated regions over the next five days. The latest SHIPS model forecast calls for wind shear to rise to the high range, 25 - 40 knots, tonight through the end of the week. This high shear, combined with the dry atmosphere to the north of Paula, should limit Paula's chances of becoming a major hurricane, since the hurricane is small and vulnerable to high wind shear. NHC is giving Paula a 27% chance of becoming a major hurricane. Shear, dry air, and interaction with the land area of western Cuba and/or the Yucatan Peninsula are likely to weaken the storm below hurricane strength later this week, as suggested by most of the intensity forecast models.

The latest set of model runs from 8am EDT (12Z) still show a variety of solutions for the future path of Paula. Steering currents in the Western Caribbean will collapse on Wednesday, potentially allowing Paula to wander in the region for many days. It is also possible that Paula could get caught up in a strong trough of low pressure predicted to traverse the U.S. this week (and spawn a Nor'easter for New England this weekend.) In this scenario, offered by the GFDL model, Paula would make a sharp turn to the east-northeast, hit western Cuba, bring tropical storm-force finds to the Florida Keys on Thursday night, then move into the Bahama Islands on Friday. NHC is making the reasonable forecast of sticking with what the majority of models are saying by predicting that Paula will stall out near the western tip of Cuba. However, residents of South Florida, Central Cuba, and the Bahamas should be prepared for Paula to come their way as a strong tropical storm on Thursday and Friday.

"Hurricane Haven" airing this afternoon
My live Internet radio show, "Hurricane Haven", will be airing again today at 4pm EDT. The call in number is 415-983-2634, or you can post a question to broadcast@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line.

Today's show will be about 30 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

Jeff Masters