Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 7:42 PM GMT on October 13, 2010
Data from an Air Force Hurricane Hunter aircraft indicates that Hurricane Paula has weakened substantially, and may now be a Category 1 hurricane. The aircraft has made three penetrations of the eye as of 3:30pm EDT, and found top surface winds of 80 mph with their SFMR instrument. Top winds seen at flight level of 10,000 feet were 92 mph, which translates to 83 mph surface winds, using the 10% reduction rule of thumb. Based on these data, it is reasonable to assume Paula is now a Category 1 hurricane with 85 - 90 mph winds, since the aircraft may not have sampled where the peak winds were occurring. Paula is in the Yucatan Channel, the narrow gap between Mexico's Yucatan Peninsula and the western tip of Cuba, and has now turned and is headed northeast towards Cuba. A rain band with heavy rains lies over the western tip of Cuba, and Cabo San Antonio on the western tip of Cuba picked up 2.80" of rain so far today from Paula. However, the winds have remained below 15 mph.
Figure 1. Radar image from the Pinar del Rio radar in Cuba at 3:15pm EDT on October 13, 2010, showing the eye of Paula near the western tip of Cuba. A strong spiral band was affecting western Cuba at this time. Image credit: Cuban Institute of Meteorology.
High wind shear due to strong upper-level winds out of the south are starting to tear up the southern portion of Paula, and satellite imagery shows the storm now has a lopsided appearance due to the shear. Low level spiral banding is no longer as impressive, and lines of low-level arc-shaped clouds are racing away from the southern portion of Paula, indicating that the hurricane has ingested dry air that has created strong thunderstorm downdrafts. Ingestion of this dry air is partially responsible for Paula's recent weakening. Water vapor satellite loops confirm the presence of a large amount of dry air on the south, west, and north sides of Paula.
Forecast for Paula
A small storm like Paula may weaken very quickly under the current 30 knots of wind shear and the dry air surrounding it. However, the latest 3pm EDT eye report from the Hurricane Hunters indicated that Paula's eyewall still remained solid, so Paula may be able to hang on for a few more hours before the shear drives dry air into the inner core and destroys the eyewall. Once that occurs, Paula should weaken more rapidly. I'd be surprised if Paula was still a hurricane on Thursday morning, even if it does not hit Cuba. Hurricane force winds extend out just fifteen miles from Paula's center, so only a very small region of coast will receive Paula's strongest winds if landfall occurs. The 11am EDT wind probability product from NHC gives Cabo San Antonio on the western tip of Cuba the highest odds of receiving hurricane force winds of any land area--a 35% chance. Key West is given a 4% chance, and Havana, Cuba, an 8% chance. These probabilities are slightly higher than they were in the 5am advisory, reflecting Paula's ability to hang tough in the face of 30 knots of wind shear. It currently appears that heavy rain will be the major threat from Paula. If Paula stalls over or near western Cuba for several days, the hurricane could easily dump more than ten inches over mountainous regions of the island.
The latest SHIPS model forecast calls for wind shear to rise to a very high 35 - 40 knots on Thursday afternoon, and remain above 25 knots for the rest of the week. This high shear, combined with the expected landfall of the center over mountainous Cuba, should be enough to destroy Paula by Sunday.
The latest set of model runs from 8am EDT (12Z) are very similar to the previous sets of runs. There are two basic solutions. One solution, championed by the GFDL and GFS ensemble mean, takes Paula just south of the Florida Keys on Friday morning, then into the Bahamas Friday afternoon. The other solution, offered by the rest of the models, is for Paula to move very slowly over western Cuba the next few days, then circle southeastwards into the Caribbean, as a strong high pressure system over the Gulf of Mexico intensifies and pushes Paula to the south. This is the more likely scenario, given the current trends in how the models are depicting evolution of the jet stream pattern over the U.S. in the coming days. However, residents of South Florida, the Keys, and the Bahamas should be anticipate the possibility of Paula coming their way as a weak tropical storm on Friday.
Elsewhere in the tropics
The NOGAPS model is predicting the formation of Tropical Storm Richard 5 - 6 days from now, in the southern Caribbean off the coast of Nicaragua, near where Paula formed. The GFS has just a strong tropical disturbance forming there.
In the Western Pacific, Tropical Storm Megi has formed, and is predicted to be a major typhoon that will threaten the northern Philippine Island of Luzon early next week.
I'll have an update Thursday morning.
Comments will take a few seconds to appear.