Invest 98L spinning up; outlook for remainder of hurricane season

By: Dr. Jeff Masters , 2:09 PM GMT on September 19, 2011

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A tropical wave midway between Africa and the Lesser Antilles (Invest 98L) continues to look well-organized on satellite imagery, with a modest amount of heavy thunderstorm activity and spin. An ASCAT pass from 8:08 pm EDT last night showed 98L was close to closing off a well-defined surface circulation. Wind shear as diagnosed by the SHIPS model is light, less than 10 knots, and is predicted to stay light to moderate through Friday. Ocean temperatures are 28 - 28.5°C, well above the threshold typically needed for a tropical storm to spin up. Water vapor satellite images show 98L is embedded in a moist environment, but there is dry air to the system's northwest. However, given the light wind shear, this dry air may not pose a hindrance to development at this time. An analysis of upper level winds from the University of Wisconsin CIMMS group shows a pattern favorable for development, with an outflow channel open to both the north and south available to ventilate the storm and allow 98L to efficiently lift plenty of moisture to high levels.


Figure 1. Morning satellite image of 98L.

The models are not very aggressive about developing 98L into a tropical depression, but most of them do show some weak development. NHC gave the disturbance a 60% chance of developing into a tropical depression by Wednesday in their 8 am Tropical Weather Outlook. Given the recent increase in spin on visible satellite images and favorable environment for development, I'd bump these odds up to 70%. 98L is currently moving little, but is expected to begin a westward motion at 10 mph today. This motion would take 98L into the Lesser Antilles Islands by Friday or Saturday. The northern Lesser Antilles would be most likely to see the core of the storm, as has been the case for all of this year's disturbances. However, a more southerly path across Barbados, as predicted by the GFS model, cannot be ruled out. Once 98L does reach the Lesser Antilles, all of the models indicate the storm will see a sharp increase in vertical wind shear due to strong upper-level winds out of the west. This shear should make it difficult for 98L to intensify as it moves though the islands.

Atlantic hurricane outlook for the rest of September
Ocean temperatures are starting to decline in the North Atlantic, though remain much above average in the Main Development Region (MDR) for hurricanes, from the coast of Africa to the coast of Central America, between 10°N and 20°N latitude. The latest departure of sea surface temperature (SST) from average plot (Figure 2) shows a large area of ocean temperatures near 1°C above average. The water temperatures were 0.8°C above average in this region during August, which is the 4th highest such reading on record. These warm waters will allow for an above-average chance of African tropical waves developing through early October. By early October, the African Monsoon typically begins to wane, spawning fewer tropical waves that tend to be weaker, and we should stop seeing development of newly-emerged tropical waves off the coast of Africa.


Figure 2. Departure of sea surface temperature (SST) from average for September 19, 2011. Ocean temperatures were about 1°C above average over much of the Main Development Region (MDR) for hurricanes, from the coast of Africa to the coast of Central America, between 10°N and 20°N latitude. In the Pacific off the coast of South America, we can see the tell-tale signature of a La Niña event, with cooler than average waters along the Equator. Also note the cooler than average waters between Bermuda and Puerto Rico, due to the passage of Hurricane Maria and Hurricane Katia. Image credit: NOAA/NESDIS.

Wind shear has been near average over the tropical Atlantic this hurricane season, and is currently at its climatological low point, which occurs in mid-September. The latest 2-week run of the GFS model shows wind shear will remain at the sort of typical low levels we usually see this time of year. With ocean temperatures at near-record warm levels, this combination would tend to favor formation of at least two tropical storms between now and the beginning of October. One inhibiting factor, though, may be the continued presence of dry, stable air over the tropical Atlantic. Hurricanes like to have an unstable atmosphere, with moist, warm air near the surface, and cold, dryer air aloft. This situation helps the updrafts in the storm grow stronger. This year, we've had unusually stable air (Figure 3.) This has really put the brakes on intensification of most of the tropical storms that have formed. The current ratio of 14 named storms but only 3 hurricanes is unprecedented in the historical record, going back to 1851. Usually, just over half of all Atlantic tropical storms intensify into hurricanes. One other factor to consider, the 30-60 day pattern of increased thunderstorm activity known as the Madden-Jullian Oscillation (MJO), looks like it will have little influence over the coming week. The MJO has been weak all month, and is predicted to stay weak for the remainder of this week.


Figure 3. Vertical instability, as measured by the difference in temperature near the surface to the bottom of the stratosphere. The atmosphere in the Caribbean (left) and tropical Atlantic between Africa and the Lesser Antilles Islands (right) has been much more stable than average this year (average is the thick black line). Image credit: NOAA/CIRA.

Forecast of the rest of hurricane season
We are past the half-way point of the Atlantic hurricane season, which typically peaks on September 10. On average, about 60% of the activity has occurred by this point in the season. Since we've already had 14 named storms and 3 hurricanes, at the current rate, we would expect to see another 8 or 9 named storms, with 1 or 2 of them reaching hurricane strength. It's pretty tough to maintain the sort of activity levels we've seen so far this year, so I am forecasting we'll see 7 more named storms during the remainder of this season, taking us all the way to "W" in the alphabet. With the unusually stable air over the Atlantic showing no signs of abating, I predict that we'll see just 2 of these storms reach hurricane strength. As far as steering currents go, the latest 2-week forecast from the GFS model doesn't show any significant changes to the jet stream pattern we've seen all summer. There will continue to be a parade of troughs of low pressure moving off the U.S. East Coast that will tend to curve any storms northwards and then northeastwards out to sea, once they penetrate north of the Lesser Antilles Islands. This pattern favors strikes on North Carolina and New England, and discourages strikes on Texas. I doubt Texas will see a tropical storm this year given this steering pattern, and considering that Texas' tropical cyclone season tends to peak in late August and early September. It is quite unusual for Texas to have a tropical storm or hurricane this late in the season, so they will probably have to look elsewhere for drought-busting rains.

Jeff Masters

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Quoting TropicalAnalystwx13:


Wow, you have a lot of troubles with your quote button. ;P




mine works
Member Since: May 21, 2006 Posts: 5091 Comments: 115085
Quoting WeatherNerdPR:

He needs glasses. Or geography class.


lol..
Member Since: July 6, 2010 Posts: 113 Comments: 32033
Quoting kmanislander:
TropicalAnalystwx13

Tried replying with the quote button but the blog seems to be messed up. The models take 98L just South of Haiti as a weak system. If that verifies then the Western Caribbean is a distinct possibility. Of course, the models are not good before we get a classified system so just something to watch for at the moment.


Wow, you have a lot of troubles with your quote button. ;P
Member Since: July 6, 2010 Posts: 113 Comments: 32033
Quoting TropicalAnalystwx13:


No, it doesn't.

He needs glasses. Or geography class.
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TropicalAnalystwx13

Tried replying with the quote button but the blog seems to be messed up. The models take 98L just South of Haiti as a weak system. If that verifies then the Western Caribbean is a distinct possibility. Of course, the models are not good before we get a classified system so just something to watch for at the moment.
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Quoting BDADUDE:
Looks set to go North of PR.


No, it doesn't.
Member Since: July 6, 2010 Posts: 113 Comments: 32033
Quoting PRweathercenter:

It could affect in many ways, i didn't saw a direct hit, just in case, Water does a lot of damage down here.
Looks set to go North of PR.
Member Since: September 3, 2008 Posts: 0 Comments: 602
Quoting TropicalAnalystwx13:


Think he means it could be Tropical Storm Ophelia by the time it is affecting the islands.
exactly, a most likely scenario if the models are right
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Quoting Hurricanes12:

It could affect in many ways, i didn't saw a direct hit, just in case, Water does a lot of damage down here.
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Quoting Hurricanes12:


Think he means it could be Tropical Storm Ophelia by the time it is affecting the islands.
Member Since: July 6, 2010 Posts: 113 Comments: 32033
Quoting kmanislander:


Hi there

Another local ??. I have been off for about 2 weeks. Some travel and some down time.

98L has my attention even though it has essentially been sitting and spinning for about 36 hours in the same place. The models are not bullish on this but we need to keep an eye on it.
I was wondering where you were but I figured when needed you would be here. Outlookchkr but don't know where in Cayman they are.
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Quoting PRweathercenter:
Tropical Storm Ophelia Could Affect Puerto Rico By Week End










???
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wow kman seeming to find more and more caymanains on here huh
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Quoting kmanislander:


Hi there

Another local ??. I have been off for about 2 weeks. Some travel and some down time.

98L has my attention even though it has essentially been sitting and spinning for about 36 hours in the same place. The models are not bullish on this but we need to keep an eye on it.


Don't think it will curve before the Western Caribbean?

I think it will curve a little farther west than what Irene did, right over Hispaniola.
Member Since: July 6, 2010 Posts: 113 Comments: 32033
Quoting stormwatcherCI:
Where in the Cayman Islands are you ?


Hi there

Another local ??. I have been off for about 2 weeks. Some travel and some down time.

98L has my attention even though it has essentially been sitting and spinning for about 36 hours in the same place. The models are not bullish on this but we need to keep an eye on it.
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Evening all. Been reading back before getting on. :(

Loved the rain last night. Had hoped for more, but it was a great storm. Amazing thin line red line of a squall that came down and through.
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They sold a LOT of Dome Foam yesterday fo sho..


Who Dat! part Deux
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Quoting Patrap:


anytime. Now I gotz to back up zee DVR as I missed MNF Kickoff.

But for a Homie, I do dat.
How bout dem Saints! And Bear fans were showed a good time too. :)
Member Since: May 26, 2011 Posts: 0 Comments: 1193
Quoting seafarer459:
Quit feeding the trolls. Your just trying to stroke your own damn egos. No one, not one, has those magical words. Nothing you say, will send a troll crying into the night. You may get a or two. But the troll, feels as if he has gotten 50. Your trying to put out a fire, with gasoline.


Words to the Wise:

Behavior that is REINFORCED will be repeated.

Behavior that is NOT REINFORCED will be extinguished.

I find the "Ignore" feature helps me to avoid the urge to respond to those who irritate us, by making them invisible! Some days I am not strong enough to resist.
Member Since: September 8, 2010 Posts: 0 Comments: 147
..Oh if you go to the blog, dont mess with Gustavo and Jesse, they hanging out in comment 2 or 3 I think.

Wah,

wah,

wahhhhhhhhh................
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Quoting FrankZapper:
Thanks,Pat


anytime. Now I gotz to back up zee DVR as I missed MNF Kickoff.

But for a Homie, I do dat.
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Quoting outlookchkr:
In the Cayman Islands, we hate anything Lo and slow to develop, Ivan wrecked us big time. We also hate the big and fast systems to start below us, no way to watch a developing system in the Caribbean, so we have to watch getting plowed from right or maybe plowed from within. It's a tough game when you are sitting on the possible storms marching through you.
Where in the Cayman Islands are you ?
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Quoting Patrap:
...my Brotha FrankZapper, Homie, check it out.

If you ever need to post the NOLA Radar, just quote my radar which is usually the first Post on my Blog, and snatch up the Img HTML Code between the quote Icons.





It should look like the above.

Post it directly n the comment box, bypassing the Image Button as its already sized .




Thanks,Pat
Member Since: May 26, 2011 Posts: 0 Comments: 1193
Click for larger image:

Appropriate tropical weather-related image.
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...my Brotha FrankZapper, Homie, check it out.

If you ever need to post the NOLA Radar, just quote my radar which is usually the first Post on my Blog, and snatch up the Img HTML Code between the quote Icons.





It should look like the above.

Post it directly n the comment box, bypassing the Image Button as its already sized .


..no charge. : )




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Quoting tropicfreak:


I apologize, I just lost it. Really stressed out today with the amount of homework I had to do, so the last thing I needed were trolls, let alone a tag team... sigh.
Yea Algebra can be quite a *****.
Member Since: May 26, 2011 Posts: 0 Comments: 1193
Evening all!

Looks to be quieter than the past few days, when the hostility level was a bit too high for me.

Assuming 98L made it into the gulf, which seems at least a possibility, given how far south it is, and how the models have it going generally westward, rather than northward, where's it likely to head from there? Texas? Mexico? Northern Gulf? Or West Florida?

I do realize it's still a long way out, and things are subject to change. Just wondering which way the proverbial wind is blowing...
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Quoting tropicfreak:


I apologize, I just lost it. Really stressed out today with the amount of homework I had to do, so the last thing I needed were trolls, let alone a tag team... sigh.


Don't sweat it. I wasn't singling you out. It was a generalized admonition to all troll feeders.
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Roke...Cat 3
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Ophelia used to iron and fold clothes and peal shrimp for my Mother.
Member Since: May 26, 2011 Posts: 0 Comments: 1193
Look at that void of dryness in the middle!
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548. JLPR2
Didn't catch much, but it does show that the LLC we were following is gone, another probably took its place were the center of 98L is now placed.

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Uhh, this is cold-core right?
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Quoting GTcooliebai:
Invest 98L should be on a west heading for a while until a point somewhere between Jamaica, Haiti, and Eastern Cuba, before it makes up its mind to turn North or continue west towards Central America, the trough on the latest GFS run doesn't really look all that strong, so it may continue on its westward heading. In all due respect future Ophelia looks like she will be a dandy, and I just have bad feelings about this one.

Looks like it will follow a Katia type of track in the end.
Member Since: September 3, 2008 Posts: 0 Comments: 602
Sorry if this has been posted before but it's relevant anyway.
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT MON SEP 19 2011

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

1. A BROAD AREA OF LOW PRESSURE HAS REFORMED FARTHER TO THE EAST ABOUT 1550 MILES EAST OF THE WINDWARD ISLANDS. SHOWERS AND THUNDERSTORMS ARE GRADUALLY INCREASING...AND ENVIRONMENTAL CONDITIONS APPEAR
FAVORABLE FOR A TROPICAL DEPRESSION TO FORM DURING THE NEXT COUPLE OF DAYS. THIS SYSTEM HAS A HIGH CHANCE...60 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES SLOWLY
WESTWARD.

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my *list*
is at
231
and still growing.
It works for me.
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Quoting twincomanche:
Patrap. LOL.
patrap is a powerhouse. Don't mess with him.
Member Since: May 26, 2011 Posts: 0 Comments: 1193
Quoting KEEPEROFTHEGATE:
next invest number 90L


Thanks Gate!
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Quoting tropicfreak:


I apologize, I just lost it. Really stressed out today with the amount of homework I had to do, so the last thing I needed were trolls, let alone a tag team... sigh.
notice there quiet now does not take long
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Quoting TropicalAnalystwx13:

http://www.nhc.noaa.gov/archive/2004/graphics/AT0 9/09.AL0904W.GIF
In the Cayman Islands, we hate anything Lo and slow to develop, Ivan wrecked us big time. We also hate the big and fast systems to start below us, no way to watch a developing system in the Caribbean, so we have to watch getting plowed from right or maybe plowed from within. It's a tough game when you are sitting on the possible storms marching through you.
Member Since: October 28, 2010 Posts: 0 Comments: 65
Quoting TropicalAnalystwx13:


You always respond to several hour old posts :P
got to love trolls
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Re: Post 502.
That is not nice!
But Ivan would follow the Everywhere Then Texas model.
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No change. No longer a low however...now classified as a disturbance.

AL, 98, 2011092000, , BEST, 0, 113N, 372W, 25, 1008, DB,

T-number from SAB below:

19/2345 UTC 11.0N 37.4W T1.0/1.0 98L

IMO, 98L still has another day or two of organization before classification takes place.
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532. JLPR2
Quoting KEEPEROFTHEGATE:
POSS.T.C.F.W.
98L/INV/XX
MARK
11.27N/37.31W


Wow, almost exactly were the new ATCF update says it is.

AL, 98, 2011092000, , BEST, 0, 113N, 372W, 25, 1008, DB

Good eye!
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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.