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Posted at 10:29 AM ET, 09/15/2010

Hurricanes keep avoiding U.S., will it continue?

By Capital Weather Gang

Hurricanes Igor and Julia at Category 4 intensity

* More nice weather: Full Forecast | Hurricane Tracking Center *

sep2010-storms.jpg
Satellite map showing three active tropical cyclones (Igor, Julia, and Karl). Source: National Hurricane Center

With the 2010 season producing tropical cyclones in rapid succession now, the United States coastline continues to remain nearly immune from the realistic threat of a direct hurricane strike. Not a single storm from this year's basket of 13 systems (11 named) has come within 75 miles of our shores at hurricane strength. In fact, only one of those 13 tropical cyclones, tropical storm Bonnie, actually made a U.S. landfall. And that was at minimal tropical storm status (40mph) near Homestead, FL, 27 miles south of Miami on the morning of July 23. One can only hope the steering currents will continue to be so kind.

In the near term, with three named systems on the active roster (Igor, Julia, and Karl), it appears the "0-for" streak will continue. Igor, the most ferocious system of the year, remains a powerful category 4 hurricane with maximum sustained winds estimated at 135 mph. Its spectacularly beautiful satellite presentation belies the tempestuous maritime conditions surely ongoing underneath its eyewall.

The variance in the track guidance is relatively small with Igor. It will very likely remain far off the mainland U.S. coast, though not before agitating the seas enough to produce large swells near the mid-Atlantic Coast over the weekend. Interests in Bermuda, however, should closely monitor the progress of Igor, as the large hurricane-force wind field may closely approach the island in a couple of days.

Julia, yet another category 4 hurricane, is the slightly disheveled looking feature on satellite imagery well to the east of Igor. With maximum winds estimated at 135 mph, Julia is expected to strengthen a little more during the next several days as it too curves northward over the central Atlantic.

According to meteorologist Jeff Masters at wunderground, it is only the second time on record there have been two category 4 hurricanes at the same time in the Atlantic. He also said Julia's 135 mph winds make it the strongest hurricane on record so far east. And hurricane researcher Phil Klotzbach at Colorado State University told CWG (Capital Weather Gang) that between August 27 and September 15 there have been four (Danielle, Earl, Igor, and Julia) category 4 hurricanes -- the most on record in such a short period.

Tropical storm Karl, the most recent addition to the season, is closer to home. Yet its proximity to Mexico, and projected track over the Yucatan, should prevent the storm from intensifying much beyond its present state (estimated at 65 mph as of Wednesday morning).

But will the steering currents for the storms later this season continue to spare the U.S. from a direct hit?

ncep-ridges.jpg
Map of average upper level wind pattern. Source: NOAA.

If the underlying shape of the atmosphere continues to feature an upper-level ridge of high pressure over the Southern Plains (shaded in orange above), as it basically has for the last month, then the answer is probably so. Many of this year's systems that have migrated westward across the tropical Atlantic have found a 'soft spot' in the upper flow over the Atlantic, between the Southern Plains high pressure and another high pressure system over the eastern Atlantic (also shaded in orange on the right side of the picture). In this zone, between roughly 75W and 45W, the winds aloft have seldom been directed toward North America.

The clockwise circulation around each of the high-altitude high pressure ridges has combined to create a northwesterly (offshore) wind and a southerly wind over the western and central Atlantic that has effectively shoved approaching Cape Verde storms (that develop off the west coast of Africa) back out to sea. In addition, the clockwise circulation around the Southern Plains system has also helped to block storms that formed in the Caribbean (like Alex, Hermine, and Karl) from turning northward in time to cross the U.S. Gulf Coast.

But if the pattern shifts just a little, toward one that moves the'weakness' in the upper-level ridging closer to Eastern North America, then the path will be cleared somewhat for a landfall. In this case, instead of a northward turn over the Central Atlantic, the recurvature could take place at a longitude much closer to home.  Some of the global weather models are hinting that this might indeed occur in the next 1-2 weeks.  We will be watching this for you closely.

(CWG's Jason Samenow contributed to this post)

By Capital Weather Gang  | September 15, 2010; 10:29 AM ET
Categories:  Tropical Weather  
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Comments

Way to jinx it, guys. I'm blaming the next one on you.

Posted by: srb52 | September 15, 2010 11:17 AM | Report abuse

Hi srb52,

I didn't jinx it. The final paragraph I submitted (not shown yet) reads:

"But if the pattern shifts just a little, toward one that moves the ‘weakness’ in the upper-level ridging closer to Eastern North America, then the path will be cleared somewhat for a landfall. In this case, instead of a northward turn over the Central Atlantic, the recurvature could take place at a longitude much closer to home. Some of the global weather models are hinting that this might indeed occur in the next 1-2 weeks. We will be watching this for you closely."

sorry for that,

greg

Posted by: gregpostel | September 15, 2010 12:11 PM | Report abuse

So what do we think the potential impact is for the Outer Banks from roughly Sunday til next weekend? Big surf and riptides but no rain would be favorable!

Posted by: CuseFan07 | September 15, 2010 1:11 PM | Report abuse

Thanks for the informative post on what's steering some of these massive systems away from the east coast. When do the Cape Verde storms typically start diminishing? It seems that October and November feature tropical systems with shorter tracks that originate closer to or within the Caribbean. I assume this is because the Atlantic water temperatures aren't quite warm enough for storm systems to cross the ocean without "losing steam," so to speak.

Posted by: meteorolinguist | September 15, 2010 1:19 PM | Report abuse

We're not through yet...this year could be like 1954.

The earlier hurricanes...Carol, Dolly and Edna...missed us that year [though Carol was extremely costly for the time in New England, toppling the steeple of Old North Church in Boston]. However, the hurricane that DID get us in 1954...HAZEL...didn't hit this area until October 15th!!!

If our weather patterns this fall resemble those of 1954, Washington ought to watch out. We could have another late heat waved...followed closely by another "Hazel". Already this meteorological fall's weather patterns bear a resemblance somewhat like those of 1954...warmer than usual early autumn.

In addition the final hurricane that year...Janet...was rather late and unusually powerful, accounting for one of the very few losses of a hurricane hunter aircraft.

Posted by: Bombo47jea | September 15, 2010 1:25 PM | Report abuse

I have no stake in the book, don't know the author, etc.. but I a few days ago, I got a copy of "Hurricanes and The Middle Atlantic States". Fascinating to revisit some storms I've experienced or been on the fringes of, e.g. Donna, Camille, Agnes, David, Isabel, etc.

As noted above, we aren't home free yet. There can be some ugly blows hereabouts in October and temps are expected to remain above average, so water temps won't cool as quickly.

One thing I am curious about is why this years storms are, for the most part, tracking so similarly? They either go to Mexico or curve to the NE in the open Atlantic. La Nina... blocking highs... what else, if anything, is at work?

Posted by: JerryFloyd1 | September 15, 2010 1:47 PM | Report abuse

Hi CuseFan07,

surf's up, but be careful. lookin' good weatherwise.

greg

Posted by: gregpostel | September 15, 2010 2:26 PM | Report abuse

Hi meteorolinguist,

That's part of it.

Also, the jetstream tends to migrate farther south as we move through Fall .. which often creates an unfavorable wind shear pattern at latitudes the Cape Verde storms ride along. In addition, the African Easterly Jetstream (one of the key ingredients in the genesis process, especially for Cape Verde storms) weakens as we head toward Winter. These are some of the reasons why we begin to see more activity in the Carribean and Gulf of Mexico in October.

By then, we start to see fronts penetrate to the Gulf and Caribbean. As these fronts dissipate over the still warm waters, weakening the veritical shear that accompanies them, the broad low-level circulation they still posess can sometimes trigger tropical development.

we have a long way to go before this season is over.

greg

Posted by: gregpostel | September 15, 2010 2:42 PM | Report abuse

Hi JerryFloyd1,

The centers of action in the subtropical atmosphere ... like the high pressure system aloft over the Southern Plains, and the semi-permanent feature over the Eastern Atlantic ... have taken residence so far this season in a place that favors the kind of track we're seeing. Global-scale mechanisms are at work to help give us the luck we've had.

Things may be shifting around a bit in the next 1-2 weeks.

greg

Posted by: gregpostel | September 15, 2010 2:50 PM | Report abuse

Fascinating, Greg, how these systems can "set up shop" and stay in place for weeks on end.

But just as last winter's snows were eventually followed by an inordinately warm spring, the current pattern could, as you note, give way to something else.

Reading the hurricane book cited above, I soon discovered that it's all that uncommon for tropical weather systems to hit drought-plagued regions. (But it was also fascinating to see how little rain can accompany these systems, especially the ones that zip through.)

Posted by: JerryFloyd1 | September 15, 2010 3:43 PM | Report abuse

Rate of speed of a tropical system does influence the rainfall in any one place. We didn't get that much rain--but a lot of wind--from Isabel.

On the other hand Texas didn't get too much wind from Allison--but the storm parked itself near or over Houston for 3 or 4 days, leading to huge amounts of rainfall and flooding. We had a somewhat similar experience in June, 1972 with Agnes, which, as a hurricane, didn't exceed Category 1.

Posted by: Bombo47jea | September 16, 2010 12:38 AM | Report abuse

The comments to this entry are closed.

 
 
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