Tropical Depression Two here?

By: Dr. Jeff Masters , 1:09 PM GMT on July 18, 2006

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The National Hurricane Center issued this special advisory at 8:20am EDT this morning:

Satellite and surface observations this morning indicate the low pressure area located about 250 miles southeast of North Carolina coast has become better organized this morning... and a tropical depression may be forming. An Air Force Reserve reconnaissance aircraft is scheduled to investigate the system this afternoon. Interests along the North Carolina and Virginia coasts should closely monitor the progress of this system.

Indeed, the first visible satellite images from this morning show a clear surface circulation developing near 32N 74W, about 250 miles south-southeast of Cape Hatteras, North Carolina. There is an impressive area of thunderstorms to the southeast side of the center of circulation. Upper level winds of 10-15 knots from the northwest are keeping any thunderstorms from building on the northwest side of the disturbance.

Water temperatures are 26 - 28C in the storm's vicinity, which is above the 26C threshold needed for tropical storm formation. The axis of the warm Gulf Stream current lies just 100 miles to the storm's northwest, so any motion towards the North Carolina coast will bring the system over very deep warm waters of 28 - 29C that should aid in intensification. The GFS computer model is indicating that wind shear will remain in the 5 - 20 knot range the next few days, which is low enough to allow some modest intensification. The exact magnitude of this shear will be critical in determining how strong this storm gets, and is difficult to predict at this time.

As we can see from the historical plot of the 15 tropical cyclones to form in July and August off the Carolina coast in July and August (Figure 3), all these systems moved north or northeast out to sea. Only one hit land, and only two got as strong as a Category Two hurricane. This storm will follow the historical trend, as a strong trough of low pressure is expected to push off the East Coast by Thursday, turning the disturbance northwards and then recurving it out to sea. North Carolina, Virgina, Maryland, and Nova Scotia appear to be the only land areas at risk from this storm.


Figure 1. Latest satellite image of the Southeast Coast disturbance.


Figure 2. Preliminary forecast model tracks for the Southeast Coast disturbance.


Figure 3. Historical tracks of tropical cyclones that formed off the Carolina coast in July and August.

Elsewhere in the tropics
A large area of thunderstorms is a few hundred miles northeast of Puerto Rico. This is associated with a tropical wave interacting with an upper-level low pressure system. Wind shear has dropped to 10 - 25 knots over this area, which is still too high to allow tropical development today, as there is a large amount of dry air in the vicinity. The system is expected to track northwest towards Bermuda and recurve out to sea.

A somewhat ragged tropical wave is near Africa, just south of the Cape Verde Islands. Water temperatures are marginal for tropical development in this region, and wind shear is high, 10-30 knots. The wind shear forecast shows the possibility of more favorable conditions later in the week if the wave can hold together as it moves westward across the Atlantic at 15-20 mph. I'm not expecting this to happen, however.

The Hurricane Center has scheduled a reconnaissance aircraft to check the Carolinas system out at 2pm EDT today. I'll be back with an update when the plane has had a chance to check the storm out.

Jeff Masters

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486. AySz88
8:16 PM GMT on July 18, 2006
In case someone hasn't said it yet, NEW POST.
Member Since: August 25, 2005 Posts: 0 Comments: 8
485. xSubmariner
8:13 PM GMT on July 18, 2006
contrary to popular belief, the speed of sound is anything but constant. Sound waves travel by the colision of molecules in the medium they are traveling. The denser the material the faster sound travels. Have your friend bang on a railroad track with a hammer while you put your ear to it some distance away. You'll here the sound come through the rail long before the sound traveling through the air. Temperature also affects the speed of sound as well as altitude. These effects are slight when traveling through the air but have great effect when traveling through things such as water. Different temperature gradients in the water cause sound to speed up or slow down which causes sound to bend. This is why submarines can hide from surface ship sonars. We make a map of sound using depths, salinity and temperature of the water we are traveling in.
484. quakeman55
8:12 PM GMT on July 18, 2006
I definitely agree with you 456. And when it does, it'll be one more thing to rub into ST's face, haha.

BTW, I thought he'd say he'd tell us when to worry about something forming. I didn't see him telling us about this one :-P
Member Since: March 31, 2002 Posts: 1 Comments: 1276
483. Cavin Rawlins
8:11 PM GMT on July 18, 2006
Member Since: July 24, 2005 Posts: 407 Comments: 19076
482. guygee
8:10 PM GMT on July 18, 2006
correction: that small ULL SW of the system it looks somewhat elongated SW to NE...
Member Since: September 16, 2005 Posts: 0 Comments: 3200
481. Cavin Rawlins
8:08 PM GMT on July 18, 2006
i beleive July will spawn one more system...all the conditions are there......
Member Since: July 24, 2005 Posts: 407 Comments: 19076
480. quakeman55
8:07 PM GMT on July 18, 2006
Now keep in mind that the recon hasn't yet sampled the entire storm, and I don't think it's yet reached the strongest convection, where there very well could be tropical storm-force winds. They showed the recon path on TWC just now and showed it go through the center and off to the NW. The strongest convection is to the N and NE of the center.
Member Since: March 31, 2002 Posts: 1 Comments: 1276
479. guygee
8:07 PM GMT on July 18, 2006
03 - Now that you mention it, I can see that small ULL SW of the system it looks somewhat elongated SW to NW...that would help explain the upper levels of the TD moving north more quickly than the low levels...the effect of that small ULL SW of the system probably doesn't extend very far, so if the TD moves away from that small ULL the current shear could be just a short-term effect.
Member Since: September 16, 2005 Posts: 0 Comments: 3200
478. txweather
8:06 PM GMT on July 18, 2006
Thanks weatherguy and Hawkeye. My mention of shear was an off the cup remark and I was beginning to doubt.(Hey i'm known for little errors). Also, from the soundings, there is some very dry aid with RH well below 50% in 500-700mb level.
476. fredwx
8:04 PM GMT on July 18, 2006
Recon reported 30Kts Max wind with min ppp of 1008mb

URNT12 KNHC 181945
VORTEX DATA MESSAGE
A. 18/19:15:40Z
B. 33 deg 08 min N
073 deg 17 min W
C. NA mb NA m
D. 30 kt
E. 180 deg 008 nm
F. 070 deg 032 kt
G. 340 deg 013 nm
H. EXTRAP 1008 mb
I. 22 C/ 200 m
J. 23 C/ 199 m
K. 23 C/ NA
L. NA
M. NA
N. 1234 / 1
O. 0.05 / 5 nm
P. AF308 0102A CYCLONE OB 14
MAX FL WIND 32 KT NW QUAD 19:08:20 Z
SLP EXTRAP FROM 1500 FT.
Member Since: June 8, 2005 Posts: 221 Comments: 261
474. Cavin Rawlins
8:02 PM GMT on July 18, 2006
aside from TD 02...what do you guys think about shear across the entire atlantic, c'bbean and Gulf...
Member Since: July 24, 2005 Posts: 407 Comments: 19076
472. HadesGodWyvern (Mod)
8:01 PM GMT on July 18, 2006
hmm Tropical Storm 06W..
Member Since: May 24, 2006 Posts: 52 Comments: 46907
471. guygee
7:58 PM GMT on July 18, 2006
Posted By: jphurricane2006 at 7:42 PM GMT on July 18, 2006.
wind shear from what? the shear is only 5kts in the area, has to be another explanation.

This must be a case of the wind shear maps being outdated or in error. Perhaps the trough is stronger than is shown, maybe it is beginning to be reinforced by the second trough over the Ohio valley? Perhaps the ULL is having an effect at the mid-levels not easily seen in the WV loops?...regardless of the cause, shear seems to be the only possible explanation.
Member Since: September 16, 2005 Posts: 0 Comments: 3200
469. Cavin Rawlins
7:55 PM GMT on July 18, 2006
we have to wait for the 5pm advisory
Member Since: July 24, 2005 Posts: 407 Comments: 19076
468. Andrew92
7:54 PM GMT on July 18, 2006
I see that circulation too jp. And thanks for the reply.
467. weatherguy03
7:54 PM GMT on July 18, 2006
Small ULL to the SW of system is creating enough S to SW shear....Link Its shutting off the outflow to the SW. Thus the west side does not look as good.

You can see it also here...Link
Member Since: July 5, 2005 Posts: 592 Comments: 29708
466. quakeman55
7:54 PM GMT on July 18, 2006
I think the EATL wave is holding together longer than most of us thought it would. It has an excellent signature on the satellite and some of the convection is starting to re-fire. If this keeps up for a while and especially if it builds up more convection, it could become TD 3.
Member Since: March 31, 2002 Posts: 1 Comments: 1276
463. Cavin Rawlins
7:50 PM GMT on July 18, 2006
Posted By: jphurricane2006 at 3:42 PM AST on July 18, 2006.
wind shear from what? the shear is only 5kts in the area, has to be another explanation.


Totally a agree, there barely any wind shear.

You are not crazy, there is spining in the lower levels of the EATL wave....cant wait to see what the NHC will say 5PM
Member Since: July 24, 2005 Posts: 407 Comments: 19076
462. Andrew92
7:50 PM GMT on July 18, 2006
Hi all. I just got back from school. Is the HH information back yet? If not when should they be? Thanks.
460. SWLAStormFanatic
7:44 PM GMT on July 18, 2006
Native, another thing I just remembered. Seems like the temperature of the lightning is different at different stages of the TStorm. I believe that a "younger" TStorm's lightning is cooler than a mature/dying TStorm. That is one reason that the thunder in a younger storm "cracks" as opposed the more of a "boom" or more bass rumble of an older storm.

I'm not 100% sure on this though, if someone has more knowledge on this please let us know.
459. Hawkeyewx
7:43 PM GMT on July 18, 2006
thelmores, just watch the visible satellite loop and you'll easily see the surface circulation
Member Since: July 5, 2005 Posts: 2 Comments: 1924
457. thelmores
7:42 PM GMT on July 18, 2006
so does that mean the COC is between the "upper" and "lower" convection blobs?
Member Since: September 8, 2005 Posts: 0 Comments: 3805
456. Cavin Rawlins
7:41 PM GMT on July 18, 2006
EATL wave sure is a player
Member Since: July 24, 2005 Posts: 407 Comments: 19076
455. txweather
7:40 PM GMT on July 18, 2006
thelmores, thats indicative of shear. What you see are thunderstorms blowing and trying to wrap but getting pushed off to the north.
454. redefined
7:39 PM GMT on July 18, 2006
>redefined- what orange county news station (i might know hat you are talking about)

WESH TV. Their website says it's channel 2?
453. FLAnative
7:38 PM GMT on July 18, 2006
SWLA - me too, watching for years that is...an interesting feature of this storm today was the preliminary wind was circling. I say that because leaves were blowing up suddenly in inverse cyclones. It was fascinating but then the lighting developed and it has been the LOUDEST I have ever heard. Truly. In all my years of Florida summer rainy seasons the loudest. Thus my questions. Thanks again, all.
Member Since: October 22, 2005 Posts: 16 Comments: 2701
452. HadesGodWyvern (Mod)
7:38 PM GMT on July 18, 2006
ya that cyclone symbol, which happens to be the symbol for a tropical storm, only represents that there is a tropical cyclone in that area, not a tropical storm.
Member Since: May 24, 2006 Posts: 52 Comments: 46907
451. Cavin Rawlins
7:37 PM GMT on July 18, 2006
jp...they must be finish...i saw the same thing when they went out in alberto and almost-berly last month
Member Since: July 24, 2005 Posts: 407 Comments: 19076
449. KShurricane
7:35 PM GMT on July 18, 2006
I think that the CIRA site is just saying that there is a tropical cyclone there, which would include a TD. In the EPac, looks like another one could be forming: TD 6 and then Emilia. Also, Daniel is now forecast to become a major hurricane by Thursday. Wasn't this supposed to be the quiet basin this year?
448. HadesGodWyvern (Mod)
7:35 PM GMT on July 18, 2006
hmm that still says 1831 GMT, is that the current time?
Member Since: May 24, 2006 Posts: 52 Comments: 46907
447. Cavin Rawlins
7:35 PM GMT on July 18, 2006
TD 02 is breaking off from the front
Member Since: July 24, 2005 Posts: 407 Comments: 19076
446. FLAnative
7:34 PM GMT on July 18, 2006
"not a very good indicator of strength unless your in a flat area with few obstructions."

Uh oh, this perfectly describes Cape Coral.

Thank you all who replied - very interesting- and for the link. Yes, shelter is the idea regardless....
Member Since: October 22, 2005 Posts: 16 Comments: 2701
444. Hawkeyewx
7:34 PM GMT on July 18, 2006
txweather is right, TD2 is really struggling right now with ssw shear and dry air. It was in better shape six hours ago when the shear appeared a bit less over the core. I see no sign the shear will lessen any today.
Member Since: July 5, 2005 Posts: 2 Comments: 1924
443. thelmores
7:34 PM GMT on July 18, 2006
man, it almost looks like the "upper convection" is splitting from the lower convection.....

what is going on here?
Member Since: September 8, 2005 Posts: 0 Comments: 3805
442. HadesGodWyvern (Mod)
7:33 PM GMT on July 18, 2006
Member Since: May 24, 2006 Posts: 52 Comments: 46907
441. Cavin Rawlins
7:33 PM GMT on July 18, 2006
jp..here's the lastest, since you cant get it...

Member Since: July 24, 2005 Posts: 407 Comments: 19076
440. guygee
7:33 PM GMT on July 18, 2006
AshleyDillo - Nice link, a keeper.
Member Since: September 16, 2005 Posts: 0 Comments: 3200
439. SWLAStormFanatic
7:33 PM GMT on July 18, 2006
Native, here are some things I've learned and observed about lightning.

-7 seconds = 1 mile

-1 or 2 very quick, short flashes of lightning (which yields a shorter duration of thunder) is indicative of a "younger" TStorm. This means that its mature (most vigorous) stage is near.

-Lightning that traverses the sky in a sprawling manor is indicative of an "old", usually past its prime TStorm. This lightning is what I call anvil lightning as it is primarily cloud to cloud, tens of thousands of feet above the surface. This yields the LLLOOOONNNNGGGG rumbling thunder that goes on and on.

*Yesterday I was in the yard observing and approaching impulse. The line of TStorms was still some 5 to 10 miles to my north. All of a sudden there was a bright flash to my SE (well ahead of the TStorm). It struck a mile or so to my SE, yielding first a loud "crackle" of thunder followed by the long rumble of thunder for probably 10 to 15 seconds. This was a bolt of lightning which most likely came off the anvil of one of the older "parent" storms behind the "new generation" storm which was directly in front of me. (Complexes of TStorms like the one I was watching yesterday produce "offspring" created by the warm air forced upward by the "parents" cooler downdraft.)

I am by no means a professional. Like I said, these are just some of my observations from years of Storm Watching.
438. mettler
7:33 PM GMT on July 18, 2006
Proximity to the lightening bolt will make it louder. Although, the speed of sound is constant it needs a medium to travel through; air is not a good medium. Therefore, as the distance from the sound source increases the amplitude of the sound waves will be diminished; the sound's energy becomes more dispersed the further it gets..until it is so dispersed you can't hear it. If the volume had nothing to do with proximity we would hear everything in our hearing range no matter how far or close
Member Since: June 21, 2006 Posts: 0 Comments: 4
437. Hawkeyewx
7:31 PM GMT on July 18, 2006
000
URNT11 KNHC 181905
97779 19034 30332 73200 02000 12016 23238 /0008
41320
RMK AF308 0102A CYCLONE OB 12

19034- Time
30332- Latitiude
73200- Logitude
02000- atlatitude
12016- previous wind direction and speed
23238- current wind direction and speed
/0008-pressure (1008mbr)




That is not quite right.

12016- wind direction and speed
23238- temp and dewpoint
Member Since: July 5, 2005 Posts: 2 Comments: 1924

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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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