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Posted at 7:30 PM ET, 10/20/2010

Another named tropical storm on the way?

By Greg Postel

* PM Update: Gloomy weather on its way out *
* Typhoon Megi update | Early fall on the Mall | Giant wind tunnel *

10:45 p.m. Update: Tropical Depression 19 (TD19) has formed according to the National Hurricane Center.

From earlier: After 18 tropical cyclones in the Atlantic and Caribbean Basins this season (of tropical depression strength and stronger) -16 of which were named - the tropics are not done yet.

Though November is just around the corner, and the conditions across these regions are gradually becoming hostile toward tropical cyclone formation, a disturbance south of Cuba (99L) is being monitored for possible development.

disturbance-99L-102010.jpg
Satellite image of tropical disturbance 99L just south of Cuba. Source: NASA.

If it becomes a tropical depression, it will be referred to as TD-19. The National Hurricane Center (NHC) gives this disturbance 70 percent odds of doing so. Should it become a tropical storm, its name will be Richard. Even if this system does not develop, heavy rains are possible over Jamaica and the Cayman Islands over the next several days as this system tends to meander around its current position.

In the satellite presentation (shown to the right), this disjointed-looking system appears to be taking a beating from high-altitude westerly winds.

ulwinds-102010.jpg
Upper level winds over the southern U.S. into the tropical Caribbean. Source: University of Wyoming.

These high-level winds, shown by the long arrows coming into the western Caribbean in the image above, are blowing aside the main thunderstorm activity and isolating 99L's low-level swirl. In a healthy system, the storms would sit atop the near-surface vortex. But in this case, they're currently more than 100 miles to its east.

disturb99l-wv-102010.jpg
Water vapor image of tropical disturbance 99L. Source NOAA.

If that is not enough, these upper-level westerlies are extremely dry, as indicated by the orange tint in the water-vapor imagery shown to the right.

As long as these dry and windy conditions near 99L persist, there will be no significant development. The high winds will shear the system apart, and the ingestion of this dry air will act to unwind any potential spinup.

However, there are some indications that by the weekend the environmental flow will relax a bit. Indeed, some of the models suggest 99L will become a hurricane in roughly the same place it is located now in less than 48 hours. I am not so bullish on this idea, but we will be watching.

By Greg Postel  | October 20, 2010; 7:30 PM ET
Categories:  Tropical Weather  
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Comments

What happens if we get past the last name on the list? Do we go to the Greek alphabet as we did in 2005?

This is happening more and more often...and better satellite coverage isn't the only cause. Back in the old days we never used to name subtropical storms which attained "tropical storm" wind speeds. This can occasionally happen outside the "official" hurricane season.

Perhaps we should do what the Joint Typhoon Warning Center used to do...keep six lists of continuously rotating names rather than starting with "A" each year. That system has its benefits, you are retiring names across the full alphabet instead of retiring dispropotionately at the beginning of the alphabet all the time. It's possible to have too few available names early in the alphabet due to successive permanent retirements [actually retiring names for only fifty or a hundred years before re-use as they used to do is a better policy...it might be nice to see another storm named Audrey, Carol, or Hazel again after the passage of half a century] and changes over the years in popular names will also tend to alleviate this problem. For instance, we should be able to add names such as Corey, Meghan, Katelyn, Jocelyn, Josh, Keanu and Salma to the Atlantic lists, and there has never been a Hurricane Marlene in the Atlantic Basin, though there has been at least one tropical cyclone named Marlene in the South Indian Ocean. As I recall, there hasn't been a tropical storm named Christine for a number of years, either. Also, Fran and Frances both have been retired, but "Franny" is still available!

Posted by: Bombo47jea | October 20, 2010 8:05 PM | Report abuse

BTW...my favorite tropical cyclone name: "Flossie"...it makes you think of dental appointments!!!

Posted by: Bombo47jea | October 20, 2010 8:09 PM | Report abuse

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