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Posted at 2:15 PM ET, 08/23/2010

Danielle unlikely to threaten U.S.

By Greg Postel

* Any showers? Full Forecast | Nats-Cubs weather *
* Where is Greenland's new ice island? | Hurricane Tracking Center *

The sixth tropical depression of the Atlantic hurricane season became tropical storm Danielle late Sunday as the circulation developed a core of sustained winds near the surface greater than 39 mph. Located in the Central Atlantic about 2,800 miles east-southeast of Jacksonville, Fla. (as of midday Monday), Danielle is moving slightly north of due west at about 16 mph. Maximum sustained winds are now estimated at 65 mph.

Infrared satellite image of Tropical Storm Danielle this afternoon. Credit: NOAA.

Recent satellite images suggest that Danielle may well be on its way to becoming a hurricane. As seen in the adjacent image, very tall thunderstorms (shaded in red) are now tightly clustered near the low-level swirl (which is obscured in this image), and a pattern of cirrus clouds (white appearance) emanates outward from these thunderstorms in many directions.

The latest hurricane track models nearly unanimously keep Danielle well out to sea, moving the storm toward the west-northwest and northwest for the next several days before recurving it north and then northeast away from the U.S. East Coast.

Keep reading for more details on the potential fate of Danielle...

The reason for this consensus in the track guidance is because the global weather models are predicting that the upper-level area of low pressure currently over the eastern U.S. will be reinforced during the next several days by a system moving in from the Northern Plains.

Arrows represent predicted winds for Thursday night at about 18,000 feet up in the atmosphere. Credit: University of Wyoming.

As depicted to the right, this accumulation of counter-clockwise spin at high altitudes close to the Eastern Seaboard will very likely protect North America from a Danielle strike -- the strong upper-level winds from the southwest off the Atlantic coast, on the east side of the upper-level low, should deflect Danielle away from the U.S.

In the big picture, it appears now that the "Cape Verde" season has come alive. Thunderstorm clusters associated with tropical weather disturbances moving westward off of Africa (and closely by the Cape Verde Islands -- hence the name) are now showing an ability to remain intact as they trek across the Atlantic. This is something that usually doesn't happen early in the summer. Danielle is indeed one of these "Cape Verde" systems. During the next six weeks, we'll be keeping a close eye on the potential development of the Cape Verde-type in the far eastern Atlantic.

While these storms are more likely to encounter hostile weather patterns during their cross-oceanic trip than, say, ones that develop closer to home in the Caribbean of Gulf of Mexico, they are sometimes the strongest if they survive.

By Greg Postel  | August 23, 2010; 2:15 PM ET
Categories:  Tropical Weather  
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Next: PM Update: Showers threaten tonight and tomorrow


It seems like the prognosis for upper lows over the east coast is a lot more important than the conditions in the eastern Atlantic.

Posted by: eric654 | August 23, 2010 4:23 PM | Report abuse

Hi eric654,

It can be, but not always.

For one, the midlatitude features have different impacts on tropical cyclones with different sizes/strengths. For example, a trough that might recurve a large, strong storm might not recurve a weaker, shallower system. And there are times when large, intense hurricanes aren't as easily "pushed around" by the upper troughs at higher latitudes.

Additionally, the tropical systems themselves can have a significant feedback on the structure and movement of the midlatitude features.

Bottom line is that they are both important, and not always equally so.

Posted by: gregpostel | August 23, 2010 8:26 PM | Report abuse

Looks as thogh Danielle is the classic example of a "fish storm"--a strong hurricane that stays completely at sea! It's not even threatening Bermuda on the currently projected track.

Must check the WWLL site to see if any lightning is being recorded out there. Lightning in and around the eyewall seems to be a good indicator of whether a tropical cyclone is strengthening.

Posted by: Bombo47jea | August 24, 2010 12:55 AM | Report abuse

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