October hurricane season outlook

By: Dr. Jeff Masters , 2:24 PM GMT on October 03, 2006

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Hurricane Isaac is no more. The storm skirted the southeast coast of Newfoundland, bringing wind gusts up to 60 mph to the island. No damage was reported.

It's a different story in the aftermath of Typhoon Xangsane for the Philippines and Vietnam. These countries suffered heavily from Xangsane. The death toll has risen to 207 in the Philippines, with hundreds injured, 146,000 homes damaged or destroyed, and 171,000 people left homeless. In Vietnam, the death toll has risen to 42, 1200 are injured, and heavy flooding is still a serious problem. Xangsane destroyed or unroofed 200,000 houses in Vietnam, causing at least $300 million in damage.

The tropical Atlantic is quiet
A non-tropical low pressure system is about 500 miles south of the Azores Islands. This low may gradually acquire tropical characteristics over the next few days as it drifts over the open Atlantic.

The computer models are indicating some development is possible by Thursday in the region between the Bahamas and Bermuda, along an old cold front. Any development here would probably move northeast out to sea, and could be a threat to Bermuda.

October Atlantic hurricane season outlook
We're in the home stretch now! For the first time since 1997, we've made it through September without a landfalling hurricane in the Atlantic (Ernesto and Florence came close, but didn't hit land as hurricanes). We now have only two more weeks of peak hurricane season left. While the season technically ends November 30, we can see that hurricane season slows down drastically around October 18 (Figure 1), thanks to increasing wind shear, cooling Sea Surface Temperatures (SSTs), and an end to the tropical waves coming off the coast of Africa. With no major changes expected to the steering patterns or general atmospheric conditions over the Atlantic the next few weeks, I believe that we will go the remainder of this season without a landfalling hurricane in the Atlantic. It still pays to be vigilant, though--recall that at this time last year, Hurricane Stan was killing 1500 people in Central America, and we still had ten more named storms to go, including the strongest hurricane of all time, Wilma.


Figure 1. Climatological hurricane and tropical storm activity for the Atlantic.

Steering pattern
The steering pattern for October over the Atlantic will remain similar to what we've seen all of hurricane season. The jet stream is expected to stay active, bringing frequent troughs of low pressure over the Atlantic that will act to recurve any storm that approaches the Caribbean or U.S. East Coast. This pattern has been in place since early June. As we progress deeper into October, the troughs grow stronger and extend further south, making it very unlikely anything developing between Africa and the Lesser Antilles Islands will make landfall. Any landfalling storms will have to form from the the remains of old fronts that push off the U.S. coast.

Dry air
Dry air should not be as detrimental for tropical cyclone formation in October compared to previous months. The Saharan Air Layer (SAL) is most prevalent over the Atlantic in June and July, and is usually not in evidence much in October. The current SAL image shows very little dry air over the tropical Atlantic. The SAL is pretty much confined to the waters near the African coast. The 2-week outlook from the GFS model shows near-normal SAL activity, with no major SAL episodes over the tropical Atlantic.

Wind shear and El Niņo
Wind shear over most of the tropical Atlantic has been near or below normal since early July. Climatologically, wind shear reaches its minimum in September, which is the same time that SSTs reach their peak. In October, wind shear normally begins to rise, which one can see in the plot for the eastern Caribbean (Figure 2, black line). The blue line in Figure 2 shows that in the past few days, wind shear has spiked to above normal values, and this is also occurring throughout the rest of the tropical Atlantic. This appears to be a temporary increase for the Caribbean; the latest 2-week wind shear outlook from the GFS model shows below-normal shear over most of the Caribbean next week. However, wind shear over the Gulf of Mexico and remainder of the tropical Atlantic is expected to be higher than normal the next two weeks.

Part of this increase in wind shear is probably due to El Niņo. An El Niņo event was officially declared by NOAA's Climate Prediction Center on September 13, when SSTs in the Equatorial Eastern Pacific reached +0.5ēC above normal, the threshold for a weak El Niņo. El Niņo continues to strengthen, and SSTs are almost a full degree Centigrade above normal now, the threshold for a moderate El Niņo. SSTs are forecast to continue much above normal (Figure 3) through the next six months (if they increase to 2ēC above normal, then this will qualify as a strong El Niņo event). It is well known that El Niņo events tend to suppress Atlantic hurricane activity by increasing upper level westerly winds at about 40,000 feet (200 mb). These strong westerly winds create a high wind shear that prevents tropical storms from forming.

Sea Surface Temperatures
Sea Surface Temperatures in the tropical Atlantic are slowly cooling now that it is October, but are still 0.5 - 1 ēC above normal. These above normal temperatures are expected to persist through the remainder of hurricane season (Figure 3).


Figure 2. Observed wind shear in 2006 (blue line) and climatological wind shear (black line) for the eastern Caribbean. Image credit: NOAA/CIRES.

Figure 3. NOAA's Sea Surface Temperature forecast for the next four months. Note the much warmer than normal SSTs over the Equatorial Eastern Pacific, indicating a moderate El Niņo event occurring. Note also that SSTs are expected to remain 0.5 - 1 ēC above normal over the tropical Atlantic for the remainder of hurricane season.

Conclusion
Because of high wind shear over the Atlantic due to the expected jet stream pattern and a strengthening El Niņo event, I am forecasting at most two more named storms this year and no hurricanes. I think it most probable we will get just one more named storm. The steering pattern we've seen all hurricane season is not expected to change much, so any storm forming during the remainder of the season is likely to stay over water. If we do get a landfalling storm, the most likely targets are the Carolinas, Bermuda, or the Gulf Coast of Florida. Perhaps the best analogue year to compare with is 1997, a strong El Niņo year, when we had two 45-mph tropical storms form in October. Neither of these storms hit land.

Jeff Masters

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534. cavemanjoe
1:38 PM GMT on October 04, 2006
Hi Utah
533. Gatorx
1:36 PM GMT on October 04, 2006
new blog
532. Utah2Miami
1:34 PM GMT on October 04, 2006
Where did everyone go....

?
531. Utah2Miami
1:27 PM GMT on October 04, 2006
Yeah Nash-

It was weird. I guess I had it coming though- what with my obstinate behavior and outspoken ways.... ;o)

Gator- I just may so everyone can see how ridiculous it was.

It wasn't until I put a pic of myself up. I considered starting a new profile and claiming to be a gorilla of a man with a hairy back and everything- maybe then the perverts will leave me alone and others will respect my opinion.

C'est la vie, right?

And... back to the weather! The Gulf and the Caribbean are a murky mess! Good thing I am flying home to Utah for the weekend tomorrow!
530. Patrap
1:24 PM GMT on October 04, 2006
..notice Okinowa on the extreme left side of the Track map..of the Typhoon...Naha,is the Capitol..and the Island is 60 nm x 11 nm..at its widest...
Member Since: July 3, 2005 Posts: 426 Comments: 128871
529. Gatorx
1:22 PM GMT on October 04, 2006
Utah-

I think you should unban or would it be disban at least one person from last night so the truth comes out.
528. Gatorx
1:21 PM GMT on October 04, 2006
Hi Nash.....I saw you on another blog this morning....there was more to the story but the abuser was banned so the comments were deleted.
527. nash28
1:21 PM GMT on October 04, 2006
Morning Utah. I guess I missed a real barn burner last night, huh?
Member Since: July 11, 2005 Posts: 190 Comments: 16972
526. Patrap
1:20 PM GMT on October 04, 2006
Typhoon turning away from Iwo Jima...something different..with the Movie coming out..Link
Member Since: July 3, 2005 Posts: 426 Comments: 128871
525. Utah2Miami
1:19 PM GMT on October 04, 2006
Good morning to everyone... rough night last night.

Still wading through the hatemail.
523. nash28
1:10 PM GMT on October 04, 2006
Morning Gator.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
522. Gatorx
1:10 PM GMT on October 04, 2006
Good morning everyone.....
520. Patrap
1:09 PM GMT on October 04, 2006
Take the Sunscreen and bail......
Member Since: July 3, 2005 Posts: 426 Comments: 128871
518. Patrap
1:04 PM GMT on October 04, 2006
King shear going to keep the GOM at Bay....it appears..kinda...shoulda..coulda..woulda..
Member Since: July 3, 2005 Posts: 426 Comments: 128871
516. cavemanjoe
12:57 PM GMT on October 04, 2006
Hi all . New here .
515. thelmores
12:53 PM GMT on October 04, 2006
mornin everybody!




well, its well east, and south.... and barely a blob... but its about the only feature i find interesting.

the shear in this area atm, seems low, and SST's are still warm..... but it will be hard for this "little blob" to gain latitude, and even if it does, it mt get "beheaded"......

seems this hurricane seaso will end just as it started..... "blob watchin" :)
Member Since: September 8, 2005 Posts: 0 Comments: 3805
514. nash28
12:49 PM GMT on October 04, 2006
Yeah, and both under a gigawatt of wind shear, so yeah.....yawn.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
513. PensacolaDoug
12:49 PM GMT on October 04, 2006
Welcome home to our wayward sons...
Member Since: July 25, 2006 Posts: 0 Comments: 581
512. PensacolaDoug
12:48 PM GMT on October 04, 2006
Two blobs to watch. Bahamas and Gulf. Yawn.....
Member Since: July 25, 2006 Posts: 0 Comments: 581
511. nash28
12:46 PM GMT on October 04, 2006
Actually, I am bored beyond belief today. Really don't have much on my plate at work today and no storms to follow.

Might fall asleep.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
510. ClearH2OFla
12:45 PM GMT on October 04, 2006
Morning Nash how are ya
508. ClearH2OFla
12:41 PM GMT on October 04, 2006
Morning all so whats the latest anything flaring up in gom or carrib.
506. Skyepony (Mod)
12:33 PM GMT on October 04, 2006

still looking blobby out there...
Interesting on the buoy too.
bbl
Member Since: August 10, 2005 Posts: 179 Comments: 38321
505. Skyepony (Mod)
12:29 PM GMT on October 04, 2006
Morning all...

Something interesting from the MLB local from the middle of the night

SAT...GFS AND ECM IN AGREEMENT THAT THE TROUGH WILL CUT OFF FROM THE
MAIN FLOW ALONG THE MID-ATLANTIC COAST. THIS SYSTEM WILL DRIVE A
FRONTAL BOUNDARY DOWN THE PENINSULA...THOUGH DEEPEST MOISTURE AND
BEST DYNAMICS WILL REMAIN WELL NORTHEAST OF THE REGION. SOME
LOW-LEVEL MOISTURE WILL PRODUCE SOME ISOLATED COASTAL SHOWERS...BUT
FOR THE MOST PART CONDITIONS WILL REMAIN RAIN-FREE.

SUN-TUE...DRY SEASON WILL ARRIVE IN EARNEST WITH REINFORCING SHOT OF
DRY AIR AND GFS 850 MB TEMPS COOLING TO 10C. COOL TEMPS REFLECTED
IN THE GFS MOS...WHICH INDICATES THAT HIGH TEMPS SUN WILL
STRUGGLE TO REACH THE LOWER 80S...DESPITE NEARLY FULL SUNSHINE.
BACKING LOW-LEVEL FLOW AROUND A DEVELOPING SURFACE LOW MAY RESULT IN
SOME COOLER TEMPS (MAINLY NORTH AND WEST OF ORLANDO) MON AND TUE
MORNINGS AS WELL. SPRAWLING AREA OF HIGH PRESSURE ACROSS THE GREAT
PLAINS WILL ENSURE THAT MEAN TEMPS REMAIN NEAR OR SLIGHTLY BELOW
NORMAL INTO TUE.

LONG TERM....HIRSCH
Member Since: August 10, 2005 Posts: 179 Comments: 38321
503. Patrap
12:28 PM GMT on October 04, 2006
..hit 91 here yesterday..feels more like early September here now..wacky..
Member Since: July 3, 2005 Posts: 426 Comments: 128871
502. Patrap
12:27 PM GMT on October 04, 2006
..looks like a wave passing on that graph kmanislander..
Member Since: July 3, 2005 Posts: 426 Comments: 128871
501. nash28
12:26 PM GMT on October 04, 2006
Very pleasant here, thank you.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
500. Patrap
12:26 PM GMT on October 04, 2006
Morning nash..how goes the weather in your neck of the woods?
Member Since: July 3, 2005 Posts: 426 Comments: 128871
499. kmanislander
12:13 PM GMT on October 04, 2006
here's another buoy thats been trending lower for the last couple of days
Maybe things are changing closer to home
Link
Member Since: August 19, 2006 Posts: 0 Comments: 15842
498. nash28
12:11 PM GMT on October 04, 2006
Morning Patrap.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
497. kmanislander
12:09 PM GMT on October 04, 2006
good morning all

just a quick check in to say welcome back to Patrap and 27windows. I saw you all on last night but I got in too late to start blogging

Will bb later when I have some time to post
Member Since: August 19, 2006 Posts: 0 Comments: 15842
496. Patrap
11:52 AM GMT on October 04, 2006
pressure graph of the Buoy Since Sept 30th....Link
Member Since: July 3, 2005 Posts: 426 Comments: 128871
495. Patrap
11:51 AM GMT on October 04, 2006
Buoy 42055 BOC...G morning...Link
Member Since: July 3, 2005 Posts: 426 Comments: 128871
494. SWLAStormFanatic
11:35 AM GMT on October 04, 2006
Good morning and welcome aboard Caveman. Glad you came out of your cave.
493. cavemanjoe
11:33 AM GMT on October 04, 2006
Hello new here
491. SWLAStormFanatic
11:25 AM GMT on October 04, 2006
Good morning. Anything to that mess in the BOC?
490. BigToe
10:57 AM GMT on October 04, 2006
Mornin Folks,
Long time , no post. I see we've made it thru the Cape Vrede season with nary a scratch. Now all we gotta do is get thru the " Back Yard Season"!! Is this a great country or what?
Member Since: June 12, 2006 Posts: 0 Comments: 239
489. nash28
10:31 AM GMT on October 04, 2006
Morning everyone!
Member Since: July 11, 2005 Posts: 190 Comments: 16972
488. Fshhead
8:24 AM GMT on October 04, 2006
yup,maaaan, long storyLOL You cannot believe what I just went through over a dying alternatorLOL
Member Since: November 19, 2005 Posts: 9 Comments: 9960
486. Fshhead
7:42 AM GMT on October 04, 2006
ahhh spent some "quality" time working on my truck today LOL. I hate it when you got to do the work yourself
Member Since: November 19, 2005 Posts: 9 Comments: 9960
484. Fshhead
7:39 AM GMT on October 04, 2006
Whats up Randrewl????
Member Since: November 19, 2005 Posts: 9 Comments: 9960

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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