Hurricane Rina a Category 2, headed towards the Yucatan

Hurricane Rina is now a Category 2 storm, headed slowly west-northwest at 3 mph towards Mexico's Yucatan Peninsula. The most recent hurricane hunter mission was at 4:32 am EDT this morning, and the next aircraft is not due into the storm until this afternoon, so we'll have to rely on satellite estimates of the storm's strength until then. Recent satellite intensity estimates suggest Rina has leveled off in intensity, with no change in strength since the last hurricane hunter mission. A murky, cloud-filled eye is visible on visible satellite loops right now. Rina also has an impressive upper-level outflow channel to the north, and very intense thunderstorms with cold clouds tops that extend up to the stratosphere. Wind shear is a moderate 15 - 20 knots due to strong upper-level winds out of the south, and these winds are injecting dry air into Rina's south side, inhibiting heavy thunderstorm development there. Water temperatures are very warm, 29 - 30°C, and these warm waters extend to great depth. Rina has brought sporadic heavy rain squalls to the Cayman Islands; George Town on Grand Cayman has received 4.76" of rain over the past three days from Rina, as of 9 am EDT this morning.


Figure 1. True-color MODIS image of Tropical Storm Rina taken at 12:15 pm EDT October 24, 2011. Two hours after this image was taken Rina had intensified into a Category 1 hurricane with 75 mph winds. Image credit: NASA.

Forecast for Rina
The hurricane hunters found Rina's eyewall had a gap in it during their 4:32 am EDT eye penetration this morning, probably caused by the moderate wind shear the storm has experienced over the past day. It is unlikely that Rina will be able to "bomb" and undergo rapid intensification unless it can close off this gap in the eyewall. Wind shear is not expected to increase until Wednesday night, so Rina still has a day and a half to continue its intensification process. Given the storm's inability to close off its eyewall so far, I expect that a Category 3 storm is the strongest that we will see. On Wednesday night, Rina will 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 Thursday.

A trough of low pressure is predicted to pass to the north of Rina late this week, which should turn Rina more to the northwest by Thursday and northeast on Friday. However, it is uncertain if Rina will be strong enough to fully "feel" the steering influence of this through and be swept to the east-northeast into Southwest Florida and the Florida Keys. If Rina makes landfall in the Yucatan Peninsula and weakens significantly, the storm will likely be too weak to get caught up by the trough and will remain trapped in the Western Caribbean. This is the solution of the latest runs of the ECMWF, UKMET, and HWRF models. However, if Rina remains strong through Friday, it is more likely to get caught up by the trough and drawn into the Florida Keys as a weakening tropical storm on Friday or Saturday. This is the solution of the latest 2 am EDT runs of the GFDL and GFS models. There is high degree of uncertainty which set of model runs will be correct.

Comparing Rina to Hurricane Wilma of 2005
Rina's intensification into a hurricane over the Western Caribbean during the last half of October brings to mind Hurricane Wilma, which also did this in 2005. Wilma went on to become a Category 5 monster, the strongest Atlantic hurricane of all-time. I don't think Rina will be another Wilma, even though the ocean temperatures and total heat content are similar to what Wilma experienced (Figure 3). Wilma had nearly ideal upper-level atmospheric conditions with an anticyclone aloft and light wind shear, under 5 knots. 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.


Figure 2. Hurricane Wilma at 8:22 a.m. CDT Oct. 19, 2005 as photographed by the crew aboard NASA's international space station as the complex flew 222 miles above the storm. At the time, Wilma was the strongest Atlantic hurricane in history, with a central pressure of 882 mb and winds of 185 mph. The storm was located in the Caribbean Sea, 340 miles southeast of Cozumel, Mexico, and had an eye just 2.3 miles in diameter, the smallest on record.


Figure 3. The total heat content of the ocean available to fuel hurricane intensification as measured by the Tropical Cyclone Heat Potential (TCHP). Top: TCHP for October 23, 2011, one day before Hurricane Rina of 2011 formed. Bottom: TCHP for October 18, 2005, the day Hurricane Wilma formed. TCHP values in excess of 80 kJ per centimeter squared (yellow colors) are often associated with rapid intensification of hurricanes. Both hurricane had similar very high levels of TCHP to help fuel intensification. Image credit: NOAA/AOML


Figure 4. Wind shear in knots for 09 UTC October 25, 2011, during Hurricane Rina of 2011 (top) and at 21 UTC October 17, 2005, the day before Wilma became a hurricane. A large area of wind shear less than 5 knots lay over Wilma as it was forming, while Rina was under wind shear of 20 knots this morning. Image credit: University of Wisconsin CIMSS.

97L north of the ABC islands
A broad region of low pressure between the ABC islands of Aruba, Bonaire, and Curacao and the Dominican Republic (Invest 97L), is moving west-northwest at 15 - 20 mph. Heavy thunderstorm activity has decreased a little since yesterday, and the activity is not organized into spiral bands, as is apparent from Curacao radar. The storm is surrounded by a large region of dry air, and this dry air is the main impediment to development. Wind shear is a low 5 - 10 knots, and is expected to remain low through Thursday, and 97L will encounter a moister atmosphere as it progresses westward into the Central Caribbean. By the time 97L reaches the region between Jamaica and Nicaragua on Thursday, the storm could develop into a tropical depression. However, none of the reliable models are predicting that 97L will develop. NHC gave 97L a 30% chance of developing into a tropical depression by Thursday, in their 8 am EDT Tropical Weather Outlook. Heavy rains from 97L should reach Jamaica on Thursday, the Cayman Islands by early Friday morning, and south-central Cuba by Friday night.

Geomagentic storm triggers brilliant aurora displays
A Coronal Mass Ejection (CME) that blasted away a portion of the sun's atmosphere earlier this week hit the Earth's magnetic field at 2 pm EDT yesterday. The resulting show of Northern Lights was observed as far south as Arkansas last night. Here in Michigan, I got a call from a neighbor's 12-year old, who was concerned that the sky was all red. Alas, the display was gone by the time I had finished explaining in far too much technical detail what was behind the event!

I'll have a new post on Rina this afternoon.

Jeff Masters