Hurricane Rina quickly formed in the Caribbean Sea yesterday afternoon. Rina became a hurricane just 21 hours after being classified as a tropical depression.

Visible satellite loops show that Rina now has an eye, and the storm is steadily expanding in size and developing an impressive upper-level outflow channel to the north. Wind shear is a moderate 15 - 20 knots due to strong upper-level winds out of the southeast, and these winds are injecting dry air into Rina's southeast side, inhibiting heavy thunderstorm development there. Water temperatures are very warm, 29 - 30°C (84-86° C.), and these warm waters extend to great depth.



RINA SETS INTENSIFICATION RECORD

Rina intensified into a hurricane just 21 hours after the first advisory was issued. This is the second fastest intensification since record keeping began in 1851. Hurricane Humberto of 2007 holds the Atlantic record for fastest intensification from first advisory issued to hurricane strength--18 hours.



Rina's formation brings this year's tally of hurricanes to six, which is average for an Atlantic hurricane season. The number of named storms this season is now seventeen, making it the 7th busiest Atlantic hurricane season since record keeping began in 1851. Only 2005, 1933, 1995, 1887, 2010, and 1969 had more named storms. However, 2011 has had an unusually low percentage of its named storms reach hurricane strength. The rare combination of near-record ocean temperatures but unusually dry, stable air over the Atlantic is at least partially responsible for this very unusual occurrence.



Rina's intensification into a hurricane over the Western Caribbean during the last half of October is reminiscent of Hurricane Wilma, which also performed such a feat in 2005. Wilma went on to become a Category 5 monster, the strongest Atlantic hurricane of all-time (with winds of 185 mph; 295 km/h).

It is unlikely that Rina will be another Wilma, even though the ocean temperatures and total heat content are similar to what Wilma experienced. Wilma had nearly ideal upper-level atmospheric conditions. Rina is experiencing 15 - 20 knots of wind shear and is also a smaller storm, and is thus more vulnerable to the effects of wind shear and dry air.

FORECAST FOR RINA



Rina will probably reach Category 3 or Category 4 strength by Wednesday.

On Wednesday, Rina will also encounter a dry airmass with high wind shear that lies over the extreme northwestern Caribbean. These conditions should weaken the hurricane, but Rina could still be a major hurricane if it makes landfall in the Yucatan Peninsula on Wednesday or Thursday.



The storm is stuck in weak steering currents, but some general guiding influences will shape her track.

A trough of low pressure (cold front) is predicted to pass to the north of Rina late this week, and now that the hurricane is expected to be a Category 2 or stronger storm, the chances for Rina to make it farther north and affect the Florida Keys and Southwest Florida have increased. The latest runs of the GFDL and HWRF models both predict that Rina will pass through the Yucatan Channel on Thursday and make landfall on Friday in the Florida Keys or extreme Southwest Florida, south of Naples. However, this is 5 or more days away, and details are going to be hard to work out until Rina starts to make a turn.



Cuba, Florida, and the Bahamas should watch Rina, as she could be a fairly potent storm coming out of the Caribbean, but conditions will likely deteriorate quickly north of about 22N, as the jet stream will be screaming directly across the Gulf of Mexico, imposing shear on any system trying to leave the Caribbean. Thus, weakening is expected after Rina recurves northeastward.

If Rina does make it to the Keys, it would likely be as a tropical storm, since wind shear, dry air, and possible land interaction with Western Cuba and Mexico would potentially knock down the storm's strength. Heavy rains from Rina should begin affecting Mexico's Yucatan Peninsula, northern Belize, and extreme Western Cuba on Wednesday.



A SECOND STORM IN RINA'S WAKE

A broad region of low pressure approaching the ABC islands of Aruba, Bonaire, and Curacao (dubbed Invest 97L by the National Hurricane Center), is moving west-northwest at 10 mph. Heavy thunderstorm activity has increased today, but the activity is not organized into spiral bands, as is apparent from Curacao radar. 97L is surrounded by a large region of dry air, and this dry air will retard development. 97L is under low wind shear less than 10 knots, and this shear is expected to remain low through Thursday. By the time 97L reaches the region between Jamaica and Nicaragua in the Central Caribbean on Thursday or Friday, the storm should find a moister environment, and could develop into a tropical depression.

The National Hurricane Center currently gives 97L a 40% chance of developing into a tropical cyclone in the next 48 hours.