Debby in the making

By: Dr. Jeff Masters , 1:42 PM GMT on August 21, 2006

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A very strong tropical wave moved off the coast of Africa Sunday. The NHC and Navy have a system where they officially designate a disturbance as an "invest"--something worth investigating. This storm is called 96L, and if there were hurricane hunters within range, they would fly the storm, as the system already appears to be a tropical depression. However, NHC typically hesitates to label these systems fresh off the coast of Africa depressions until they hold together for at least a day. Many such systems fall apart within their first day over water. The waters under the wave are 27-28 C, which is .5-1.5 degrees C above the 26.5 C threshold for tropical cyclone formation--not great, but good enough. Wind shear is a low 5-10 knots. There is a large area of dry air and Saharan dust to the wave's north, and this will likely be a major inhibiting factor for this wave once it moves north of 15 N latitude.


Figure 1. Visible satellite image at 8am EDT Mon Aug 21 from the European satellite. Image credit: Navy Research Lab.

The wave is impressive on satellite imagery this morning--low level spiral banding has formed, and there is a clear low-level rotation of the clouds. There is also some upper-level outflow developing on the east side. We don't have a recent QuikSCAT pass to judge the surface winds. The GFS, NOGAPS, and GFDL models develop the wave into a tropical storm; the UKMET does not. I expect that the model consensus is correct--this system will be Tropical Storm Debby by Wednesday. All the models predict that the storm will pass well north of the Lesser Antilles Islands. The storm may bring tropical storm conditions to the Cape Verde Islands Tuesday and Wednesday, as it moves west or west-northwest at 15 mph just south of the islands. Although it is too early to be certain, the Cape Verde Islands will probably be the only land areas the storm will affect. The preliminary model runs point to a track that will eventually recurve the storm out to sea before affecting any other land.

Sea surface temperatures cool to below the 26.5 C threshold tropical systems prefer north of the Cape Verdes Islands, so once the system moves north of about 15 N latutide, it may weaken. There is also a lot of dry air and Saharan dust to the north that will cause trouble for it. The GFDL model does intensify the storm to a Category 1 hurricane, then weakens it as the dry air and cooler SSTs take their toll.


Figure 2. Preliminary model tracks for the Atlantic disturbance 96L.

Elsewhere in the tropical Atlantic, there are no threat areas to discuss, and the computer models are not forecasting any development through Wednesday.

Jeff Masters

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647. kylejourdan2006
9:27 PM GMT on August 21, 2006
Waver Vapor Imagery:
Member Since: July 18, 2006 Posts: 32 Comments: 1521
644. kylejourdan2006
9:24 PM GMT on August 21, 2006
Looking at the water vapor imagery, TD4 won't be having problems with Saharan dust for some time.

Member Since: July 18, 2006 Posts: 32 Comments: 1521
643. StormJunkie
9:20 PM GMT on August 21, 2006
Afternoon all.

I see we are still wondering if the high will block TD4 or not. I am also intersted to see how TD4 acts out past the 144hr time frame. I am not completely convinced that it will not move W late in the forecast period.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
641. hurricane23
9:15 PM GMT on August 21, 2006
Guys read my thoughts on what might happen with TD4.Again the reason it will eventually turn to NW is to a couple of short waves the will weaken the ridge.In my opinion this has a very little chance of even affecting the islands.
Member Since: May 14, 2006 Posts: 8 Comments: 13807
640. Oreodog
9:13 PM GMT on August 21, 2006
Ihave27:

Your new Delta Chi name is Bronson -- because I believe you have a CV death wish!
639. swlaaggie
9:13 PM GMT on August 21, 2006
Gotta go. Everyone look east and start blowing. "Debbie does the US" just doesn't sound right.

Have a great evening.
Member Since: April 26, 2006 Posts: 0 Comments: 1032
638. WPBHurricane05
9:12 PM GMT on August 21, 2006
Tazmanian:

I didnt see that Ioke is now a cat. 3 hurricane, and then when i posted that i saw they upgraded it
Member Since: July 31, 2006 Posts: 56 Comments: 8112
636. snotly
9:11 PM GMT on August 21, 2006
Wow! 15 miles! STL. I was going by memory, thought I might stick my foot in my mouth. But Still! It looks like I didn't give Wilma full credit after all. So if the wind field increased and the intensity was somewhat maintained, I would argue that we had an even more powerful storm after the pinhole eye, just not as intense. I would assume that it is it the fact that its a balancing act to keep all the power compacted into a 15 mile gradient that makes these eyes so short lived. You reach a certain threshold and the storm flings itself apart.
Member Since: August 27, 2005 Posts: 0 Comments: 686
635. dtrobert
9:11 PM GMT on August 21, 2006
IOKE: CAT 4 by tomorrow. I personally have never seen a CPAC hurricane that strong, but then again I've only been following the tropics for a few years.

000
WTPA22 PHFO 212053
TCMCP2

HURRICANE IOKE FORECAST/ADVISORY NUMBER 8
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI CP012006
2100 UTC MON AUG 21 2006

AT 11 AM HST...2100Z...A HURRICANE WARNING HAS BEEN ISSUED FOR JOHNSTON ISLAND. A HURRICANE WARNING MEANS THAT HURRICANE CONDITIONS ARE EXPECTED WITHIN 24 HOURS.

HURRICANE CENTER LOCATED NEAR 13.0N 166.3W AT 21/2100Z POSITION ACCURATE WITHIN 25 NM

PRESENT MOVEMENT TOWARD THE NORTHWEST OR 315 DEGREES AT 11 KT

ESTIMATED MINIMUM CENTRAL PRESSURE 960 MB
MAX SUSTAINED WINDS 100 KT WITH GUSTS TO 120 KT.
64 KT....... 45NE 40SE 35SW 40NW.
50 KT....... 80NE 65SE 60SW 75NW.
34 KT.......140NE 110SE 100SW 130NW.
12 FT SEAS..140NE 110SE 100SW 130NW.
WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL
MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT.

REPEAT...CENTER LOCATED NEAR 13.0N 166.3W AT 21/2100Z AT 21/1800Z CENTER WAS LOCATED NEAR 12.6N 165.9W

FORECAST VALID 22/0600Z 14.3N 167.6W
MAX WIND 115 KT...GUSTS 140 KT.
64 KT... 45NE 40SE 35SW 40NW.
50 KT... 85NE 65SE 60SW 75NW.
34 KT...145NE 115SE 105SW 135NW.

FORECAST VALID 22/1800Z 16.0N 169.4W
MAX WIND 115 KT...GUSTS 140 KT.
64 KT... 45NE 40SE 35SW 40NW.
50 KT... 85NE 65SE 60SW 75NW.
34 KT...145NE 115SE 105SW 135NW.

FORECAST VALID 23/0600Z 17.2N 170.7W
MAX WIND 110 KT...GUSTS 135 KT.
64 KT... 45NE 40SE 35SW 40NW.
50 KT... 80NE 65SE 60SW 75NW.
34 KT...140NE 110SE 100SW 130NW.

FORECAST VALID 23/1800Z 18.2N 171.7W
MAX WIND 100 KT...GUSTS 120 KT.
50 KT... 75NE 65SE 60SW 70NW.
34 KT...130NE 110SE 100SW 120NW.

FORECAST VALID 24/1800Z 19.7N 173.5W
MAX WIND 90 KT...GUSTS 110 KT.
50 KT... 70NE 65SE 60SW 65NW.
34 KT...125NE 110SE 100SW 115NW.

EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 200 NM ON DAY 4 AND 225 NM ON DAY 5...AND FOR INTENSITY NEAR 20 KT EACH DAY

OUTLOOK VALID 25/1800Z 21.3N 175.4W MAX WIND 80 KT...GUSTS 100 KT.

OUTLOOK VALID 26/1800Z 22.8N 177.8W MAX WIND 70 KT...GUSTS 85 KT.

REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 13.0N 166.3W

NEXT ADVISORY AT 22/0300Z

$$
FORECASTER KODAMA
634. GainesvilleGator
9:11 PM GMT on August 21, 2006
Hmm, anybody see Stormtop today? Didn't he say just a few days ago that there would not be any tropical storm formation in the Atlantic Basin for the rest of August? I think he might have added ... maybe at the very end of August. Never say never when prediction tropical storm formations.
Member Since: September 11, 2005 Posts: 4 Comments: 745
633. swlaaggie
9:11 PM GMT on August 21, 2006
Follow-up Oreo.

Yea, it doesn't surprise me that he loves LSU. I am surrounded with LSU grads and fans. They loved their time there as well. It truly is a good school and their engineering program is exceptional. I've had several who have worked with or for me in the past.
Member Since: April 26, 2006 Posts: 0 Comments: 1032
632. Tazmanian
9:11 PM GMT on August 21, 2006
Posted By: WPBHurricane05 at 2:07 PM PDT on August 21, 2006.
i see now it changed


what changed
Member Since: May 21, 2006 Posts: 5091 Comments: 115254
631. hurricane23
9:10 PM GMT on August 21, 2006
Guys the stronger this system gets the higher the chance for it to recurve out sea.Models take this system on a almost NW fashion as a couple of mid-latitude short waves move through Atlantic and erode the ridge.after it moves away from the cape verde islands i expect this system to only be a shipping problem. Lets see what happens.

Here are some models for TD 4.Showing a WNW direction to NW.


Member Since: May 14, 2006 Posts: 8 Comments: 13807
630. nash28
9:08 PM GMT on August 21, 2006
That's what I have been saying all day about the ridge. It is still a ways from 55 or 60W, so things can rapidly change. Many times this year, the models have forecasred a weakening along the ridge and it never turned out that way.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
629. sporteguy03
9:07 PM GMT on August 21, 2006
leftovers,
yeah I been watching it , no local mets in FL want to talk about it, it should give FL a soaking!!!I think its amazing how some people can write off a system so quickly in the East ATL after it develops, I already heard a meterologist in Central Florida say its not gonna hit us it won't hit the U.S. either, hmm, If I was a weatherman I might say this system is moving WNW and we will keep an eye on it to see if there are any deviations to push it West, that kind of lets peoples guard down too easily just say to the people in SC with Hugo and the weatherman said it won't hit us.
Member Since: July 7, 2005 Posts: 0 Comments: 5361
628. swlaaggie
9:07 PM GMT on August 21, 2006
Oh my goodness Oreo. At least you have family Ags to keep you in check.

My 14 year old wants to go to UT. Desperately trying to talk him out of it. Told him burnt orange just wouldn't look good on him at all. :)

Actually, I would be very proud if he was a UT grad. I'm headed to the bathroom now. LOL!
Member Since: April 26, 2006 Posts: 0 Comments: 1032
626. WPBHurricane05
9:07 PM GMT on August 21, 2006
i see now it changed
Member Since: July 31, 2006 Posts: 56 Comments: 8112
625. category6
9:06 PM GMT on August 21, 2006
I already bought all the bread at my local grocery store
624. StoryOfTheHurricane
9:06 PM GMT on August 21, 2006
i said it wouldnt surprise me just cuz thats what the models are saying, but i believe it will remain on a westerly track until its steared differently
623. WPBHurricane05
9:06 PM GMT on August 21, 2006
o well the CPHC for me says 85MPH
Member Since: July 31, 2006 Posts: 56 Comments: 8112
622. Cavin Rawlins
9:05 PM GMT on August 21, 2006
Major Hurricane IOKE

Member Since: July 24, 2005 Posts: 407 Comments: 19076
621. WPBHurricane05
9:04 PM GMT on August 21, 2006
nash28 the high pressure looks to strong for it too curve soo soon, i say by about 60W just before the islands, that it should curve out
Member Since: July 31, 2006 Posts: 56 Comments: 8112
620. Tazmanian
9:04 PM GMT on August 21, 2006
by looking at the photo weather456 it look like it moveing W passing the Cape Verde you think?
Member Since: May 21, 2006 Posts: 5091 Comments: 115254
618. StoryOfTheHurricane
9:04 PM GMT on August 21, 2006
if you live anywhere west of this system, don't assume your out of the path until it takes that turn
617. ihave27windows
9:04 PM GMT on August 21, 2006
I guess the monkeys on the Cape Verde Islands are seeking higher ground....thank God they have monkeyvision....
Member Since: July 19, 2005 Posts: 108 Comments: 14931
616. TheLimey
9:03 PM GMT on August 21, 2006
The discussion from the NHC says that the ridge will slide to the East in the next few days and erode, due to interactions with some mid latitude short waves. This will allow the TD to move more northwards.
615. WPBHurricane05
9:03 PM GMT on August 21, 2006
where u get that sprocketeer?? about Ioke
Member Since: July 31, 2006 Posts: 56 Comments: 8112
614. nash28
9:03 PM GMT on August 21, 2006
Ok, please tell me (us) why a turn north wouldn't surprise you. What steering data are you seeing that is bringing you to this conclusion?
Member Since: July 11, 2005 Posts: 190 Comments: 16972
613. Tazmanian
9:03 PM GMT on August 21, 2006
Weather456 what dos W mean?
Member Since: May 21, 2006 Posts: 5091 Comments: 115254
612. Cavin Rawlins
9:03 PM GMT on August 21, 2006
TD 04

Member Since: July 24, 2005 Posts: 407 Comments: 19076
610. rwdobson
9:02 PM GMT on August 21, 2006
even if it goes west a while, the odds are it will turn north well before reaching the US coast.

link to steering winds: Link
Member Since: June 12, 2002 Posts: 0 Comments: 1589
609. IKE
9:02 PM GMT on August 21, 2006
Posted By: leftovers at 4:00 PM CDT on August 21, 2006.
No one is mentioning the Car. wave. Seems to be holding its own unlike yesterday.


It'll be a GOM wave/blob tomorrow.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
608. Sprocketeer
9:01 PM GMT on August 21, 2006
Ioke just exploded in the Central Pacific, skipping Cat. 2 status altogether. Jumped from 85 mph to 115 mph in one advisory.

As for soon-to-be-Debby, looks like all she's gonna do is cause some noise pollution for a few fish. Still, first Cape Verde storm of the season.
607. Oreodog
9:01 PM GMT on August 21, 2006
swla:

Yep. Now, remember, I'm an orange-blood. But, I have enough aggies in my family that I lost all signs of rabies a while back. He chose to go there in Pet. Eng. and loves it.
606. Cavin Rawlins
9:01 PM GMT on August 21, 2006
Lets see if TD 04 chooses the west or go by the computer models.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
605. SavannahStorm
9:01 PM GMT on August 21, 2006
If you watch the 5-day steering current loop, you'll notice the ridge building, not getting weaker.
Member Since: September 22, 2005 Posts: 18 Comments: 2343
604. WPBHurricane05
9:00 PM GMT on August 21, 2006
i see a fish storm, just not a curve so soon
Member Since: July 31, 2006 Posts: 56 Comments: 8112
603. StoryOfTheHurricane
9:00 PM GMT on August 21, 2006
a turn north wouldnt surprise me tho
601. StoryOfTheHurricane
9:00 PM GMT on August 21, 2006
im saying westward movement too
599. nash28
8:59 PM GMT on August 21, 2006
Ok, I see we have TD 4 and most everyone already says fish storm. Is someone seeing something that I am not?

The ridge looks pretty well in place, so please educate me on how she can bust through and move NW or N and curve...
Member Since: July 11, 2005 Posts: 190 Comments: 16972
598. Cavin Rawlins
8:59 PM GMT on August 21, 2006
The steering maps says westward movement....
Member Since: July 24, 2005 Posts: 407 Comments: 19076

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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.