Tropical weather analysis - October 23, 2012

By: KoritheMan , 6:30 AM GMT on October 23, 2012

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Tropical Storm Sandy formed over the southwest Caribbean on Monday. As of the latest NHC advisory, the following was posted on Sandy:

Wind: 45 mph, with higher gusts
Location: 12.9°N 78.7°W
Movement: Stationary
Pressure: 998 mb

Sandy is an intensifying tropical cyclone. The tropical storm appears to be quickly developing a central dense overcast, and the associated convection is quite vigorous at this time. A large curved band has become apparent east of the center; I expect this band will wrap cyclonically into the center during the overnight hours, and probably help to invigorate the circulation even more.

Figure 1. Latest infrared satellite image of Tropical Storm Sandy. Image credit: NOAA

Sandy is currently in a very favorable for strengthening, even rapid. The SHIPS rapid intensification parameter at 0z shows a 45% chance of a 35 kt increase in wind speed during the next 24 hours. This model is generally good at recognizing when the large scale environment is conducive to such episodes, and looking at water vapor imagery, a well-defined anticyclonic pattern aloft has set up over Sandy. In addition, the underlying waters are very warm, and extent to a rather large depth. Finally, the ambient area encompassing Sandy is extremely moist. Climatologically, this area has bred some rather infamous hurricanes this time of year, the most recent being Hurricane Paloma in 2008. Sandy may be no exception. Interestingly, water vapor imagery shows a newly-developed upper low centered over central Cuba. The GFS insists that this feature will weaken and move eastward, but this does not appear to be happening at the present time, and even if it does, the low is distant enough from Sandy so that it will provide more diffluence than shear, which is evident by the expanding outflow in the western quadrant of the storm. This feature could play a major role in rapid intensification of the storm during the next 24 hours.

While I am not going to go all the way to 85 kt in 24 hours (which would be a 45 kt increase, complimenting the SHIPS), that degree of intensification is entirely possible if current trends continue. My intensity forecast is just shy of this threshold, and shows an intensifying hurricane making landfall in Jamaica in 48 hours. There is a chance Sandy could become a major hurricane prior to reaching Jamaica. Thereafter, interaction with Jamaica and Cuba, along with a significant increase in vertical shear, should be enough to progressively weaken Sandy. The global models generally show Sandy losing tropical characteristics near the end of the forecast period, so a transition into a subtropical storm is shown at day five.

Water vapor, UW-CIMSS steering data, and upper air data suggest that Sandy is south of a well-established mid-level ridge over the western Atlantic. The net result has been a practically stationary tropical cyclone. A weak shortwave trough is getting ready to move off the United States east coast, and the southwesterly flow associated with this feature is expected to turn Sandy to the north-northeast later today. While the large-scale models are in good agreement on this, there are still some notable differences after the system emerges from northern Cuba. The ECMWF brought the system rather close to the Florida east coast at 12z, and the GFS, which had previously insisted on a trajectory that carried the system out to sea on a path well to the east of Florida, has also moved a little farther westward in the longer range. I mentioned in my last forecast that Sandy could take a similar trajectory to Hurricane Michelle in 2001, and the models have started to reflect that thinking. It should be noted that there is considerable uncertainty in long-range forecasts.

My own track forecast is similar to the National Hurricane Center except a little slower during the first 48 hours, and farther west after that.

Sandy is expected to produce torrential rains over portions of Haiti, Jamaica, and eastern Cuba. On the current track, rainfall will be limited in the Cayman Islands since they will be on the weaker side of the storm.

5-day intensity forecast

INITIAL 10/23 0300Z 40 KT 45 MPH
12 hour 10/23 1200Z 50 KT 60 MPH
24 hour 10/24 0000Z 65 KT 75 MPH
36 hour 10/24 1200Z 80 KT 90 MPH...SOUTH OF JAMAICA
48 hour 10/25 0000Z 70 KT 80 MPH...INLAND OVER JAMAICA
72 hour 10/26 0000Z 60 KT 70 MPH...OVER WATER
96 hour 10/27 0000Z 50 KT 60 MPH
120 hour 10/28 0000Z 50 KT 60 MPH...SUBTROPICAL

5-day track forecast

Figure 2. My 5-day forecast track for Sandy.

Tropical Depression Nineteen

Tropical Depression Nineteen also formed on Monday, and as of the latest NHC advisory, the following was available on the cyclone:

Wind: 35 mph, with higher gusts
Location: 23.0°N 51.8°W
Movement: N at 9 mph
Pressure: 1006 mb

Deep convection has developed over the low-level center this morning, which is an indication that the tropical cyclone is getting better organized. Unfortunately, there have been no new microwave passes to fully ascertain the inner structure of the cyclone.

Figure 3. Latest infrared satellite image of Tropical Depression Nineteen. Image credit: NOAA

Vertical shear is currently fairly light over the system, and the underlying waters are warm. This should allow for some strengthening of the tropical cyclone for the next 36-48 hours. Subsequently, the global models show the shear significantly increasing as the storm begins to interact with a large extratropical low. Concurrent with decreasing sea surface temperatures, the system is forecast to become extratropical in about three days, and then become absorbed by the aforementioned non-tropical system at day five.

The depression appears to be in the process of recurving, as the motion no longer looks uniformly northward. A turn to the northeast is expected to begin later today, followed by acceleration as the westerlies pick up the storm. The upper-level trough forecast to perform the recurve is a relatively shallow one, but it should still prove adequate to cause the depression to exit the stage. Although the four day forecast point shows a tropical cyclone nearing the Azores, the depression is forecast to become absorbed by the north Atlantic extratropical cyclone before it can make landfall in that archipelago.

5-day intensity forecast

INITIAL 10/23 0300Z 30 KT 35 MPH
12 hour 10/23 1200Z 35 KT 40 MPH
24 hour 10/24 0000Z 40 KT 45 MPH
36 hour 10/24 1200Z 45 KT 50 MPH
48 hour 10/25 0000Z 50 KT 60 MPH
72 hour 10/26 0000Z 45 KT 50 MPH...EXTRATROPICAL
96 hour 10/27 0000Z 35 KT 40 MPH...EXTRATROPICAL

5-day track forecast

Figure 4. My 5-day forecast track for Tropical Depression Nineteen.

Eastern Pacific disturbance

An area of disturbed weather continues several hundred miles south-southwest of Acapulco. This system has not become any better organized over the last 24 hours, and although the shear is light, the large size of the disturbance appears to be inhibiting development.

This low is expected to move westward and still has the potential for some development, but nothing interesting is likely to happen for at least the next three days.

The global models are less enthusiastic about the threat to Baja, probably because they depict a system that is slower to develop. That seems like the more realistic in light of current organization trends.

Probability of development in 48 hours: 20%

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4. WunderAlertBot (Admin)
11:29 AM GMT on October 24, 2012
KoritheMan has created a new entry.
3. GeorgiaStormz
1:12 PM GMT on October 23, 2012
Member Since: February 11, 2012 Posts: 0 Comments: 9769
2. KoritheMan
7:07 AM GMT on October 23, 2012
Quoting Slamguitar:
Great post Kori! Sandy looks like she wants to be a trouble maker. Here's to hoping that doesn't happen.

It's possible we'll have two retired storms this year (Isaac will undoubtedly be the first).
Member Since: March 7, 2007 Posts: 603 Comments: 21792
1. Slamguitar
6:49 AM GMT on October 23, 2012
Great post Kori! Sandy looks like she wants to be a trouble maker. Here's to hoping that doesn't happen.
Member Since: July 2, 2011 Posts: 0 Comments: 1183

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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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