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Posted at 11:32 AM ET, 10/23/2012

Tropical Storm Sandy threatens five different countries in coming days, including U.S.


Tropical Storm Sandy (NASA)
Just six hours after the initial advisory on tropical depression 18 yesterday morning, it was upgraded to tropical storm Sandy, the 18th named storm of the season. Sandy is projected to become a hurricane and more models suggest it will threaten the U.S. compared to yesterday. But it will impact Jamaica, Cuba, Haiti and the Bahamas first.

A hurricane warning is in effect for Jamaica, while a hurricane watch is in effect for the eastern half of Cuba. A tropical storm watch has been issued for Haiti and the Bahamas.

At the same time, Tropical Depression 19 formed well to its northeast and is likely to become Tropical Storm Tony today. The climatological secondary peak in Atlantic activity is certainly being reinforced this season.

Tropical storm Sandy

Sandy is in the one area in the Atlantic basin where conditions are ideal for a tropical cyclone to form and significantly strengthen right now. It’s currently about 300 miles south-southwest of Kingston, Jamaica and becoming better organized by the hour.

The vertical shear (difference between low-level winds and upper-level winds) is astoundingly low at just 6mph, the sea surface temperature is 85F (29.5C), the ocean heat content is practically infinite (no concern of upwelling cold water), it’s far from land, and on top of all of that, it’s basically just sitting in place soaking it all up.

Predicted to become a hurricane within the next 24 hours, its maximum sustained winds are 50 mph. It has actually been drifting more to the southwest, giving even more time in these ideal strengthening conditions before eventually getting steered north toward Jamaica.

The official forecast from the National Hurricane Center brings Sandy northward starting later today, passing over Jamaica on Wednesday morning, then eastern Cuba on Thursday morning.

The exact effect that Jamaica and Cuba have on the storm’s intensity is unknown. some storms lose a lot of punch after crossing over these mountainous islands, while others don’t. Regardless, after Cuba, the Bahamas is next on its tour, and that encounter is expected on Thursday night into Friday morning. Keep in mind that these times are for the center of the storm; rainbands and damaging winds will occur typically 12-18 hours before and after the center passes.


Five-day rainfall forecast. (HPC)
Southeastern Florida could experience tropical storm conditions on Friday and Saturday when Sandy is at its closest approach to that area. The 5-day rainfall forecast from NOAA’s Hydrometeorological Prediction Center (HPC) shows an accumulation of about 3” through Sunday morning in southeast Florida.

Will Sandy strike the U.S. East Coast?

After the Bahamas, Sandy should have a couple of days off the southeast U.S. coast before the track becomes uncertain. This is where ensembles from the leading global models come in handy.

Due to the inherent chaos in the atmosphere, as well as observation and model errors, forecasts become much less reliable the further out you look. By 7-10 days, it’s not prudent to rely heavily on a single run and extract details from it. Instead, think more in terms of probabilities and generalities. This graphic shows the forecast tracks from three models’ (GFS, UKMO, CMC) ensembles.


Ensemble members from three global models (0000 UTC cycle), each one further west than the other. The ECMWF model (not shown) is similar to the UKMO.

There is a real possibility that the northeast U.S. could experience a very significant storm by the middle of next week, but also a possibility that the storm will be well out to sea. However, given the potential impact the former scenario would have, it’s worth exploring and monitoring extremely closely. Recent model runs have been trending toward the East Coast impact scenario.


Comparison of the surface pressure field from the deterministic runs of GFS (top) and ECMWF (bottom) valid on Sunday evening.
The GFS model remains the furthest east and “safest” option for the U.S, though some ensemble members still produce major impacts in the northeast U.S. next week.

But the other models don’t agree, and all show a much more dangerous western track along the coast, not too different from Irene in 2011. It would also gain energy from an advancing trough. While it may lose some of its tropical characteristics, it could become an extremely large and potent subtropical/extratropical cyclone with the capability of bringing damaging winds and heavy rain (and snow??) well inland, and significant storm surge and beach erosion all along the entire eastern seaboard.

If the models continue to bring the storm along this track, preparations should begin within the next couple of days and it should not be underestimated. We will continue to watch the model forecasts continuously.

Tropical depression 19

The disturbance that I mentioned yesterday that was several hundred miles east-northeast of the Leeward Islands was upgraded to Tropical Depression 19 at 5 p.m. EDT yesterday, and appears to be on its way to becoming Tropical Storm Tony later today.

At 11 a.m. EDT this morning, the intensity was estimated to be 35 mph and forecast to intensify to 50 mph within the next couple of days as it heads northeast toward the Azores. After Tony, there are only two more names on the traditional list (Valerie and William), then it’s on to the Greek alphabet if necessary. That has only been done once before: in 2005 when six names were required from the Greek alphabet.

* Brian McNoldy is a senior researcher at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science.

By Brian McNoldy  |  11:32 AM ET, 10/23/2012

Categories:  Latest, Tropical Weather

 
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