A mid-Atlantic tropical wave worth watching; more on this year's steering currents

By: Dr. Jeff Masters , 1:19 PM GMT on July 03, 2007

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A tropical wave in the mid-Atlantic, near 9N 38W, has grown more organized since yesterday. This system has been labeled "96L" by the NHC. The wave has a small closed circulation, as seen on both visible satellite loops and this morning's 4:28am EDT QuikSCAT pass. Winds from QuikSCAT were as high as 35 mph. Wind shear is about 10 knots, and is forecast to fluctuate between 10 and 20 knots in the region over the next two days. This is low enough wind shear to allow some slow development. Sea surface temperatures are 27-28 C, which is above the 26 C minimum temperature tropical storms typically need to form. There is one cluster of strong thunderstorms near the center of circulation, but dry air to the north appears to be limiting the thunderstorm activity. The Saharan Air Layer (SAL) lies just 50-100 miles north of the storm's center of circulation, as seen in water vapor satellite loops. The GFS model does indicate a tropical depression might form here, but does not have a very good handle on it, since it is showing far too slow of a forward speed. Our other three reliable models, the NOGAPS, UKMET, and ECMWF, do not develop the system. Climatologically, formation of a tropical depression in this region of the Atlantic this time of year is quite rare. Given this fact, plus the presence of so much dry air near a relatively small circulation, I am not expecting this to become a tropical depression. Movement of 96L will be just north of due west over the next few days at 15 mph, as seen in the model forecast plots (Figure 1).


Figure 1. Computer model forecast tracks for 96L.

More on steering currents for this hurricane season
Yesterday, I posted my bi-monthly hurricane outlook, for the first half of July. Since it was getting a bit long, I presented only a short steering current analysis. More follows here. There are several ways to look at steering currents. I presented the position of the surface high pressure system known as the Bermuda High (or Bermuda-Azores High). Another way is to study how close to the surface a pressure of 500 millibars (mb) is found. When there is low pressure aloft, due to a trough of low pressure, the height at which a pressure of 500 millibars is found moves closer to the surface. If one plots up the "500 mb height anomaly"--the difference of where a pressure of 500 mb is found above the surface, compared to the average height from a climatology of the past 30 years--one gets a good measure of where above or below average storminess occurred. Higher than average 500 mb heights imply less storminess and possible drought conditions. The 500 mb height anomaly plot for June 2007 (Figure 2) shows higher than average heights across the southwestern U.S., where drought and high temperatures were observed in June. Lower than average 500 mb heights imply an above normal preponderance of troughs of low pressure and thus storminess. This was the case over Texas and Oklahoma in June. If these troughs are over the Atlantic, they act to recurve hurricanes out to sea at the longitude they are at. This only occurs if a hurricane penetrates far enough north to "see" the southernmost part of the trough of low pressure. Typically, this happens northward of about 20 degrees north latitude. Figure 2 shows lower than average 500 mb heights occurred over most of the Atlantic, meaning there were many more troughs of low pressure than usual. Had any hurricanes occurred over the Atlantic north of about 20 degrees north latitude, they would have gotten caught up in one of the troughs and recurved out to sea. The latest 2-week forecast from the GFS model shows a continuation of this above average frequency and intensity of troughs of low pressure over the Atlantic--much like we saw in 2006. Thus, we can expect any tropical cyclones that penetrate north of about 20 degrees north latitude to get recurved. This will very likely be the case for 96L, if it ever becomes a tropical storm.


Figure 2. Difference in height (in decameters, or tens of meters) from average of the 500 millibar height above the surface for June 2007. Image credit: NOAA/ESRL.

Jeff Masters

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1778. CJ5
3:49 PM GMT on July 04, 2007
Well, there is no problem seeing the COC on the visible now lol even a defined eye. Its not looking good, though.
Member Since: July 4, 2007 Posts: 0 Comments: 1755
1776. BoyntonBeach
1:45 PM GMT on July 04, 2007
A shot from a snowy day in Colorado...

A shot from Colorado..
Member Since: July 5, 2006 Posts: 0 Comments: 1
1775. stormpetrol
1:18 PM GMT on July 04, 2007
Oh forgot to mention Happy Independence Day to all Americans.Enjoy and be safe in your travels.
Member Since: April 29, 2007 Posts: 0 Comments: 7716
1774. nash28
1:16 PM GMT on July 04, 2007
Oh, and I would like to say Happy Independence Day to everyone. Do something nice for a vet today. Be proud to be an American! I know I am.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1773. stormpetrol
1:14 PM GMT on July 04, 2007
Am I right in thinking from looking at sat loop that 96L is gaining forward speed and even though the low level circulation is more exposed it looks stronger, bigger and more pronounced, also looks like its catching up fast with the convection to the SW of the COC.
Member Since: April 29, 2007 Posts: 0 Comments: 7716
1772. WPBHurricane05
1:13 PM GMT on July 04, 2007
NEW BLOG
Member Since: July 31, 2006 Posts: 56 Comments: 8112
1771. nash28
1:13 PM GMT on July 04, 2007
Morning all. Looks like 96L is still fighting. Dry air is really having its way though. If it can keep convection and wrap around, should be TD3 sometime today.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1770. Drakoen
1:09 PM GMT on July 04, 2007
that is a possiblility Pensacola drug. They would have been able to do a RECOn flight on it.
Member Since: October 28, 2006 Posts: 57 Comments: 29942
1769. PensacolaDoug
1:05 PM GMT on July 04, 2007
I'll repeat what I said at this time yesterday.

It already is a a TD. (It meets the meteorlogical definition.) The NHC hesitates to make it official because the prognosis is so bleak. They will hold off declaring it until it is obviously a threat. Is there anyone here who doubts that this would already have advisories on it if it was in the GOM?

Member Since: July 25, 2006 Posts: 0 Comments: 553
1768. pottery2
1:01 PM GMT on July 04, 2007
Good Day, and Happy Independence to you Americans.
96 L has an arrow pointing at me this morning.?? What does it all mean, I ask myself.?

Some have said ( me included ) that it would end up in the South Carib. Isles.
Well, I gues some guesses are right. !!!!!!!
Still; time for this to develop, fizzle, turn north etc etc.

Have a great one all. I'm out mostly. Some of us have to work man !!!
1767. hurricanealley
1:01 PM GMT on July 04, 2007
when will 96L move into moist air
Member Since: March 26, 2006 Posts: 8 Comments: 971
1766. Patrap
1:00 PM GMT on July 04, 2007
America is Proud to Celebrate Her Independence today..May God keep US safe and Strong thru the coming Year.

Happy 4th of July..!


6
Member Since: July 3, 2005 Posts: 421 Comments: 127701
1765. Patrap
1:00 PM GMT on July 04, 2007
I own PHI stock..shes a good company for Louisiana.. Fouchoun Chevron dock.
Member Since: July 3, 2005 Posts: 421 Comments: 127701
1764. GulfPilot
12:57 PM GMT on July 04, 2007
This "blurb" in the Atlantic has garnered the attention of Oil interests in the Gulf of Mexico this morning.

Due to extreme deep water drilling (in up to 6000 ft of water), the advanced warning needed to pull out of a drilling well and evacuate can be as much as seven days. Therefore, if the blurb in the Atlantic decides to spin up, and follows the current model tracks, we will probably be looking at some heavy evacuation flying by the middle of next week.

As a note of interest... Last year was the first time in 24 years that we did not have a single evacuation for storms in the Gulf of Mexico. Most observers do NOT expect a repeat this year!
Member Since: August 15, 2005 Posts: 2 Comments: 13
1763. catastropheadjuster
12:47 PM GMT on July 04, 2007
HAPPY 4TH OF JULY EVERYONE.
Member Since: August 24, 2006 Posts: 21 Comments: 3657
1762. philliesrock
12:42 PM GMT on July 04, 2007
The CMC is calling for 97L/TD 3/TS Chantal to move off the African coast next Monday.
Member Since: June 29, 2006 Posts: 65 Comments: 3197
1761. Drakoen
12:41 PM GMT on July 04, 2007
i don't think the dry air is gonna move away. In fact its moving in on the system. thats why the system doesn't have alot of convection at the present time.
Member Since: October 28, 2006 Posts: 57 Comments: 29942
1760. hurricanealley
12:40 PM GMT on July 04, 2007
is the dry air going to move away from 96L
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1759. Drakoen
12:38 PM GMT on July 04, 2007
theres a mid level circulation. Its the 4th of july alot of people won't be on..
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1758. lweetz
12:36 PM GMT on July 04, 2007
Is there anything is the disturbance of the central Florida coast? It looks to have a little circulation.
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1756. Drakoen
12:23 PM GMT on July 04, 2007
what interests me is that it is near after where it is and it is building convection, this time yesterday it was losing convection, because of the dinural phase.
Member Since: October 28, 2006 Posts: 57 Comments: 29942
1755. Drakoen
12:21 PM GMT on July 04, 2007
The Madden-Julian Oscillation (MJO) is an equatorial traveling pattern of anomalous rainfall that is planetary in scale.

The MJO is characterized by an eastward progression of large regions of both enhanced and suppressed tropical rainfall, observed mainly over the Indian Ocean and Pacific Ocean. The anomalous rainfall is usually first evident over the western Indian Ocean, and remains evident as it propagates over the very warm ocean waters of the western and central tropical Pacific. This pattern of tropical rainfall then generally becomes very nondescript as it moves over the cooler ocean waters of the eastern Pacific but reappears over the tropical Atlantic and Indian Ocean. The wet phase of enhanced convection and precipitation is followed by a dry phase where convection is suppressed. Each cycle lasts approximately 30-60 days.

The MJO is also known as the 30-60 day oscillation, 30-60 day wave, or intraseasonal oscillation.

(wikipedia)
Member Since: October 28, 2006 Posts: 57 Comments: 29942
1754. Altestic87
12:20 PM GMT on July 04, 2007
Drak it might become a depression before it reaches 300 miles east of the Antilles but thats about it.

I think the ridge about 50/100 miles ESE of Bermuda will weaken a little to allow it to move WNW into the Bahamas instead of the Caribbean. But that's my 2.

And another thing, what does MJO mean?
1753. Drakoen
12:15 PM GMT on July 04, 2007
its starting to build some heavy convection on the west side as the low moves under the clouds again.
RB Loop
Member Since: October 28, 2006 Posts: 57 Comments: 29942
1752. Drakoen
12:12 PM GMT on July 04, 2007
StormW is going into the carribbean. I don't believe that this system will strength untill it moves within a few hundred miles of the lesser anitilles
Member Since: October 28, 2006 Posts: 57 Comments: 29942
1751. WPBHurricane05
12:12 PM GMT on July 04, 2007
You to Storm!!
Member Since: July 31, 2006 Posts: 56 Comments: 8112
1749. WPBHurricane05
12:10 PM GMT on July 04, 2007
I think you did pretty good Storm. The models are starting to shift south into the Caribbean.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
1748. Altestic87
12:09 PM GMT on July 04, 2007
God I hope it develops. Hope it keeps winning its battle against the dry air.
1746. amazinwxman
12:06 PM GMT on July 04, 2007
I agree Drakoen warmer waters isn't the problem 96L needs to overcome/move away from the dry air to it's north then it could strengthen but not until then and I don't believe it will become our TD (just my 2 cents).
1745. Drakoen
12:00 PM GMT on July 04, 2007
...SPECIAL FEATURE...
A 1013 MB LOW PRES CENTER NEAR 11N42W...OR ABOUT 1200 NM E OF
THE LESSER ANTILLES. CONVECTIVE ACTIVITY ASSOCIATED WITH THE LOW
AS DECREASED SOME WITH SCATTERED MODERATE TO ISOLATED STRONG
WITHIN 120 NM SW QUADRANT.
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1744. Drakoen
11:59 AM GMT on July 04, 2007
you can see the SAL over the northern side of the system but notice theSAL gets weaker as it progress west.
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1743. Drakoen
11:56 AM GMT on July 04, 2007
Posted By: WPBHurricane05 at 11:52 AM GMT on July 04, 2007.

As it moves further west toward warmer waters convection should increase.


yea as it moves out of the area of SAL, that currently over the northern side of the system.
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1742. Drakoen
11:54 AM GMT on July 04, 2007
lol westward is actually better
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1741. WPBHurricane05
11:53 AM GMT on July 04, 2007
But that is if the dust doesn't kill it first.
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1740. Srt4Man
11:53 AM GMT on July 04, 2007
Happy 4th All!
1739. WPBHurricane05
11:52 AM GMT on July 04, 2007
As it moves further west toward warmer waters convection should increase.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
1738. amazinwxman
11:51 AM GMT on July 04, 2007
I agree with you Tay and Dr. masters (he knew from the start what he was talking about and was right).
1737. Alleyoops
11:50 AM GMT on July 04, 2007
Photo Sharing and Video Hosting at Photobucket

Happy 4th of July, Jeff...
Member Since: April 18, 2007 Posts: 190 Comments: 29421
1736. Caymanite
11:49 AM GMT on July 04, 2007
Good morning all. Seems like 96L is starting to get a taste of the rum in the Windwards and starting to stagger. Hopefully this will continue as I really dont like the southerly shift of the models which puts it deeper into the warmer waters of the Caribbean. Will be interesting to see if it can survive the day. I am starting to have my doubts.
Member Since: December 9, 2005 Posts: 0 Comments: 315
1735. Drakoen
11:47 AM GMT on July 04, 2007
Member Since: October 28, 2006 Posts: 57 Comments: 29942
1734. TayTay
11:46 AM GMT on July 04, 2007
I've been saying it from the start that dry air will prevent 96L from really developing. I still think it will fizzle. LLC is exposed again.
1733. Drakoen
11:45 AM GMT on July 04, 2007
i was talking about it entering the carribbean not its actual strength.
Member Since: October 28, 2006 Posts: 57 Comments: 29942
1732. amazinwxman
11:44 AM GMT on July 04, 2007
Drakoen are you talking about 96L? If so how is it even more dangerous now with dry air beating it up bad, it's convection down in the ITCZ, and an exposed center?
1731. Drakoen
11:42 AM GMT on July 04, 2007
Member Since: October 28, 2006 Posts: 57 Comments: 29942
1730. Thundercloud01221991
11:40 AM GMT on July 04, 2007
hopefully it does
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1729. Drakoen
11:40 AM GMT on July 04, 2007
.
Member Since: October 28, 2006 Posts: 57 Comments: 29942
1728. Drakoen
11:38 AM GMT on July 04, 2007
yea thundercloud. but look at the convection it can move into. Its still not dead. It now even more dangerous.
Member Since: October 28, 2006 Posts: 57 Comments: 29942

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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.