Tropical weather analysis - October 24, 2011

By: KoritheMan , 2:50 AM GMT on October 25, 2011

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Rina

Rina rapidly intensified into a hurricane today. From the time the first advisory was issued until this afternoon, Rina took approximately 21 hours to go from a tropical depression to a hurricane. This is the second fastest intensification rate for a tropical cyclone transitioning from a tropical depression to a hurricane, behind only Hurricane Humberto of 2007, which finished the feat in just a little over 14 hours. As of the most recent NHC advisory, the following was posted on Rina:

Wind: 80 mph, with higher gusts
Location: 17.2°N 83.3°W
Movement: WNW at 3 mph
Pressure: 985 mb
Category: 1 (Saffir-Simpson Hurricane Scale)

There still appears to be some shear over the hurricane, as outflow is still somewhat restricted to the southeast, especially relative to other quadrants. Nonetheless, given its rapid intensification today, the environment is clearly more favorable than I thought.



Figure 1. Latest infrared satellite image of Hurricane Rina, courtesy of NOAA's Satellite Services Division (SSD).

Upper-level winds are forecast to remain at favorable levels, and now that Rina has become a hurricane much quicker than I thought, there is no reason to assume that the storm will not eventually become a major hurricane. Right now, I predict Rina will top out as a 105 kt hurricane. However, given that the hurricane is relatively small, it is prone to rapid intensity fluctuations, up or down. The current southeasterly shearing regime which still lingers may retard rapid intensification in the near-term, despite SSTs near 30C directly underneath the hurricane.

Now that the shortwave trough that was causing the poleward movement yesterday has departed, the subtropical ridge has managed to rebuild to the north of the hurricane. On Wednesday, a significant trough is forecast to emerge from the Rockies, imparting an abrupt and swift weakening of the subtropical ridge. This synoptic evolution favors Rina turning northward as it approaches the Yucatan Peninsula in about two days, followed by a sharp turn to the northeast or east-northeast as the hurricane comes under the influence of southwesterly flow in association with the aforementioned trough/cold front.

Yesterday, I was thinking that central Florida was at greater risk than south Florida. However, that was before the unexpected intensification began today. Now that it has, Rina will be a much deeper system than I predicted yesterday, which throws a wrench into my previous track forecast. A deeper system will be more inclined to follow the deep-layer tropospheric flow, which will tend to carry it into the south Florida area. Although the models have generally been showing a weaker trough in today's runs, I am not apt to deviate significantly from my previous one. If anything, I am a good deal farther south than yesterday given the vertical depth of the hurricane.

It should be noted that confidence in the forecast track of Rina is not particularly high given continuous run to run variability amongst the global and dynamical models, and also because we don't know just how deep Rina might get. A weaker system would tend to move a little farther west before feeling the pull from the trough. Thus, if for some reason Rina struggles, the cyclone will likely come farther up the Florida peninsula.

Also, even though Rina is expected to reach south Florida as a tropical cyclone, strong vertical shear associated with the cold front, along with the very dry airmass currently in place across the Gulf of Mexico, should prevent Rina from reaching the United States as anything more than a minimal hurricane.

Given that Rina is forecast to reach the Yucatan Peninsula as a major hurricane, the potential exists for heavy damage and widespread electrical disruption. Western Cuba could also experience sustained hurricane force winds; at the very least, sustained tropical storm force winds appear likely for that section of the country.

Watches or warnings will likely be required for portions of Belize and the Yucatan Peninsula tomorrow.

Invest 97L

An area of low pressure over the southeastern Caribbean ("97L") about 100 miles north of Margarita Island, Venezuela has shown a marked increase in convection today, although this convection is not directly over the center, and is not well organized, according to satellite and doppler radar pictures from the island of Curacao.

The outflow pattern associated with this disturbance is steadily improving, and an anticyclone appears to be developing atop the surface center. This signifies that upper-level winds have relaxed. The biggest impediment to development is an area of dry air that surrounds the system. However, the tremendous surge of convection today has allowed for the system to insulate itself pretty well from this normally negative factor. Nevertheless, if the circulation tightens up (which is inevitable if deep convection persists), 97L may entrain some of this dry air, which will slow development.

The odds of this system becoming a tropical cyclone have increased since yesterday, and I now put the odds of this eventually becoming a tropical cyclone at 40%. A generally west-northwest path through the eastern and central Caribbean is expected over the next few days.

Regardless of development, heavy rainfall and gusty winds will likely impact portions of northern Venezuela as well as Aruba, Bonaire, and Curacao through tonight. These rains may be capable of causing localized flooding in some areas.

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2. Caymum
12:01 PM GMT on October 25, 2011
Hi, am a lurking mother of a small baby in Cayman. Thanks for this and for your thoughtful contributions over the last week to Dr M's blog. I have to say I don't like the look of the week ahead, with Invest 97l and Rina doing who knows what kind of a dance...


Any thoughts on the Cayman situation would be appreciated!
Member Since: October 25, 2011 Posts: 0 Comments: 0
1. LakeWorthFinn
3:16 AM GMT on October 25, 2011
Thanks Kori :)
Member Since: October 6, 2005 Posts: 67 Comments: 7421

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About KoritheMan

I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.

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