TD 13 intensifying; Katia may pass uncomfortably close to U.S.

By: Dr. Jeff Masters , 3:28 PM GMT on September 02, 2011

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Tropical Depression Thirteen formed last night over the Northern Gulf of Mexico and is slowly intensifying, but isn't in a hurry to go anywhere. What TD 13 will do is dump torrential rains along the northern Gulf Coast over the next three or more days. So far, rain amounts along the coast have mostly been below one inch. At New Orleans Lakefront Airport, just 0.32" inches of rain had fallen from TD 13 as of 10 am CDT. Some coastal regions have received up to two inches, according to radar rainfall estimates. TD 13 is generating a large area of 30 - 35 mph winds over the Gulf of Mexico. At 7:20 am CDT, winds at the Mississippi Canyon 711 oil rig were southeast at 47 mph. This is above tropical storm force, but the wind instrument was 348 feet (106 m) above the ocean surface, and winds near the surface were probably considerably lower, near 35 mph. Latest surface wind observations from an Air Force hurricane hunter aircraft support leaving TD 13 as a tropical depression. Long range radar out of Mobile, Alabama shows heavy rain showers building along the northern Gulf Coast, but these rain showers are not well-organized into spiral bands. Strong upper-level winds out of the west-northwest are creating a moderate 10 - 20 knots of wind shear over TD 13, keeping the storm's heavy thunderstorms disorganized and pushed to the east side of the storm. However, latest satelllite loops show TD 13 is becoming increasingly organized, with a respectable spiral band forming on the southeast side, and an increase and areal coverage of heavy thunderstorm activity. This is very likely to be a tropical storm later today.


Figure 1. Radar-estimated rainfall from TD 13 from the New Orleans radar.


Figure 2. U.S. drought conditions on August 30. The rains from TD 13 have the potential to bring major drought relief to drought-stricken portions of the coast. Note how Eastern North Carolina is no longer in drought, thanks to the rains from Hurricane Irene. These rains also came close to putting out a persistent fire that had been burning in the Great Dismal Swamp near the Virginia/North Carolina border. Image Credit: U.S. Drought Monitor.

Forecast for TD 13
TD 13's large size, ill-formed circulation center, and the presence of dry air on its west side due to an upper-level trough of low pressure argue against rapid intensification of the storm for the next three days. Also tending to slow intensification will be the slow movement of the storm, which will allow cold water from the depths to rise to the surface, thanks to wind and wave action. Tropical cyclones strongly cool the water's surface when they pass over it, as seen in the time vs. depth chart of sea surface temperatures during Hurricane Irene's passage along the New Jersey coast (Figure 3.) However, the Gulf of Mexico has some very warm waters near TD 13 that extend to great depth (Figure 4), so the surface cooling imparted by TD 13 will be less than that seen for Hurricane Irene. As TD 13 moves closer to the coast, more and more of its circulation will be over land, which will also slow intensification. NHC's 11 am EDT wind probability forecast for TD 13 gave the storm a 23% chance of intensifying into a hurricane by Sunday. Assuming TD 13 does not attain hurricane strength, wind damage and storm surge damage will likely not be the main concern--fresh water flooding from heavy rains will be the most dangerous impact. Also of concern is the possibility of tornadoes. NOAA's Storm Prediction Center is currently not highlighting the Gulf Coast in their "slight risk" area for severe weather, due to the lack of enough solar heating to create instability. However, there will be plenty of wind shear in the lower part of the atmosphere that can potentially create spin in the coastal thunderstorms, and it is possible that as TD 13 intensifies, it may be able to generate several dozen tornadoes.

Coastal Louisiana, Mississippi, Alabama, and the extreme western Panhandle of Florida will likely receive very heavy flooding rains that will intensify Saturday and peak on Sunday. These rains should be able to put out the stubborn marsh fire east of New Orleans that has brought several days of air quality alerts to the city, but may cause moderate to severe flooding problems in other areas. The latest rainfall forecast from NOAA Hydrological Prediction Center shows that a large area of 15+ inches of rain is expected over Southeast Louisiana and coastal Mississippi. The region is under moderate drought, so flooding problems will be delayed compared to what we'd normally expect from heavy rains of over a foot. Flash flood watches are posted for New Orleans and surrounding areas, and rainfall amounts of 1 - 3 inches per hour are possible in some of the heavier rain squalls. Ocean temperatures are near record warmth, 88°F (31°C), which will provide plenty of moisture for heavy rains, and plenty of energy to help TD 13 strengthen into a strong tropical storm. Steering currents will be weak in the Gulf this weekend and early next week, which will likely make the motion of TD 13 erratic at times.


Figure 3. EPA, in conjunction with Rutgers University and the NJ Department of Environmental Protection, has an Autonomous Underwater Vehicle (AUV, aka the Glider) deployed off the coast of NJ (since early August) continuously monitoring ocean temperature, density, salinity, sound velocity and dissolved oxygen at different depths. The AUV's path and data are displayed at the following website: http://marine.rutgers.edu/cool/auvs/index.php?did =221&view=imagery. The plot of temperature versus time above shows that in the weeks prior to the arrival of Irene, the ocean was heavily stratified, with warm waters of 24 - 26°C (75 - 79°F, red colors) extending from the surface to a depth of 10 - 15 meters. A sharp thermocline existed at a depth of about 15 meters, and ocean temperatures were colder than 14°C (57°F, dark blue colors) below the thermocline. The strong winds and high wave action of Hurricane Irene on August 28 - 29 stirred up cold water from the depths to the surface, cooling the surface waters to 17 - 19°C (63 - 67°F). In the days since the hurricane, surface waters have begun to warm again. Thanks go to Kevin Kubik, Deputy Director of the Division of Environmental Science and Assessment for EPA Region 2, for making me aware of this data.


Figure 4. The total amount of heat energy in the ocean available to fuel a tropical cyclone, in kilojoules per square centimeter of surface area. Tropical cyclones that move over ocean areas with TCHP values in excess of 70 - 90 kJ/cm^2 commonly undergo rapid intensification. Waters that are warm to a great depth have the highest TCHP, and the Loop Current that brings warm water northwards from the Caribbean to the Gulf of Mexico usually has the highest TCHP values in the Atlantic. Currently, we have an eddy that broke off from the Loop Current earlier this summer, now located a few hundred miles south of the Louisiana coast, that also has high TCHP values. Image Credit: NOAA/AOML.

Hurricane Katia
Hurricane Katia is continuing its long trek across the Atlantic Ocean today, and will not pose a danger to any land areas over the next five days. Katia is still struggling with dry air and moderate wind shear of 10 - 20 knots. Latest satellite loops show surface-based arc-shaped clouds racing to the southwest away from Katia's core, a sign that dry air is penetrating into Katia's thunderstorms and creating strong downdrafts that are robbing the storm of heat and moisture. Katia is over warm ocean waters of 28.5°C, and these waters will increase in temperature to 29°C over the next five days. Katia will pass well north of the region of cooler waters stirred up by the passage of Hurricane Irene last week.

The models are split on when the upper-level trough of low pressure bringing the wind shear to Katia will move away, and the storm may spend two more days battling wind shear and dry air before the upper-level trough pulls away to the north and allows Katia to intensify more readily. It is still unclear how much of a threat Katia may pose to the U.S., but it is becoming increasingly clear that Katia will pass uncomfortably close to the U.S. East Coast. The trough of low pressure currently steering Katia to the northwest will lift out early next week, and a ridge of high pressure is expected to build in, forcing Katia more to the west. This decreases the danger to Bermuda, but increases the danger to the U.S. A second trough of low pressure is expected to begin affecting Katia by the middle of next week, and will potentially recurve the storm out to sea before it hits the U.S. However, the models differ widely on the strength and timing of this trough. Meteorologist Grant Elliot of Australia's Bureau of Meteorology in Perth pointed out to me yesterday that the long-range forecast for Katia has more than the usual amount of uncertainty, due to the inability of the computer models to agree on what will happen to Tropical Storm Talas in the Western Pacific. Talas is expected to hit Japan early on Saturday as a strong tropical storm, then race northwestwards into the Bering Sea off the coast of Alaska. Talas is then expected to transition into a powerful extratropical storm in the waters south of Alaska. This storm will create a ripple effect downstream in the jet stream, all the way to North America, by early next week. The timing and amplitude of the trough of low pressure off the U.S. East Coast expected to potentially recurve Katia out to sea next week is highly dependent upon the strength of Tropical Storm Talas during its transition to an extratropical storm. The computer models are not very good at handling these sorts of transitions, leading to more than the usual amount of uncertainty in the long-range outlook for Katia. It will probably be another 2 - 3 days before the models will begin to converge on a solution for the long-term fate of Katia. Dr. Bob Hart's Historical Tropical Cyclone Probability web page suggests shows that tropical storms in Katia's current position have a 17% chance of hitting North Carolina, a 21% chance of hitting Canada, a 13% chance of hitting New England, and a 55% chance of never hitting land. One almost certain impact of Katia on the U.S. will be large waves. Long period swells from Katia will begin affecting the Bahamas on Sunday night, then reach the Southeast U.S. by Monday morning. By Tuesday morning, the entire U.S. East Coast will see high surf from Katia, and these waves will increase in size and power as the storm grows closer. Given the slow movement of Katia as it approaches the coast, plus its expected Category 1 to 3 strength as it approaches, the storm will probably cause extensive beach erosion and dangerous rip tides for many days.

94L
A well-organized low pressure system with a surface circulation but limited heavy thunderstorm activity due to high wind shear is 450 miles south of Halifax, Canada. This disturbance, (94L), is headed northeast out to sea, and is being given a 60% chance of developing into a tropical depression by NHC. 94L is under a high 25 - 30 knots of wind shear, but this shear is expected to fall to the moderate range, 10 - 20 knots, by Saturday morning. However, sea surface temperature will fall from 27°C today to 25°C Saturday morning underneath 94L, and the storm will have a very short window of time to get organized enough to get a name. At this point, it's really a subjective judgement call on whether or not 94L is already a tropical storm.


Figure 5. A Portlight volunteer works to clear storm debris from Hurricane Irene in Hollywood, Maryland.

Portlight disaster relief effort in Maryland
Hurricane Irene heavily damaged the town of Hollywood, Maryland, when a tornado cut off electric power, water, and phone service. Portlight and Team Rubicon volunteers arrived before emergency personnel, after following up on a local tip. What they found was an isolated area whose plight was unknown to the larger community. Most residents were trapped at their homes by heavy debris. Portlight and Team Rubicon worked for two days to clear paths to each address, extract vehicles from debris, and cut down trees that constituted safety hazards. Portlight also instructed local residents how to operate and maintain chainsaws and safely clear debris. No other volunteer organizations or emergency personnel arrived at any time, and Portlight succeeded in meeting the specific needs of the underserved, unserved, and forgotten. Visit the Portlight blog to learn more; donations are always welcome.

I'll have a new post each morning over the coming holiday weekend; wunderground meteorologists Angela Fritz, Rob Carver, and Shaun Tanner will be handling the afternoon and evening posts. Have a great holiday weekend, everyone!

Jeff Masters

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1387. JGreco
Has Lee even moved. Seemed like its been wandering around stationary so far.
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Quoting nolacane2009:


where are you located?
im in new orleans east near that darn marsh fire
Member Since: July 25, 2010 Posts: 0 Comments: 2473
1385. Patrap
Kinda looks like all those, er..4 trees we saw in Up state NY.

Damage BeauCoup
Member Since: July 3, 2005 Posts: 414 Comments: 125572
1384. pcola57
Quoting P451:
This ought to clear things up a little...




LOL LOL!!!
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Well, all of you who are lucky enough to get rain out of Lee, please post photos because we here in Texas have forgotten what rain looks like.
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1381. Patrap
A Lil Puff of Convection beginning near the Western CoC



Member Since: July 3, 2005 Posts: 414 Comments: 125572
As of 15 minutes ago, a buoy NW of the center...

24-hour plot - Wind Direction Wind Direction (WDIR): ENE ( 60 deg true )
24-hour plot - Wind Speed Wind Speed (WSPD): 32.1 kts
24-hour plot - Wind Gust Wind Gust (GST): 36.9 kts
24-hour plot - Air Temperature Air Temperature (ATMP): 80.6 °F
24-hour plot - Dew Point Dew Point (DEWP): 75.2 °F
24-hour plot - Visibility Visibility (VIS): 5.2 nmi
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Quoting bigwes6844:
oh boy we got a huge rain band getting ready to hit us in a few hours.


where are you located?
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Member Since: July 25, 2010 Posts: 0 Comments: 2473
1375. pcola57
Quoting StAugustineFL:
All quiet for now.........



Maybe too Quiet ehh?
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Katia, on August 31st.
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Quoting Charmeck:
Did Katia take a little jog northward in the 5:00 PM update? Sure looks it from my tracking map ---


Got her center right about where it's supposed to be... almost half way between today's 18Z forecast point and tomorrow's 06Z.
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oh boy we got a huge rain band getting ready to hit us in a few hours.
Member Since: July 25, 2010 Posts: 0 Comments: 2473
All quiet for now.........

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Quoting OracleDeAtlantis:

You are right, but of course they'll be criticized if they say that, because of the people who might cancel their travel plans to the beaches.

A lot of folks wait until the kids go back to school, and they relax in September, before the water gets cold.

Heck that's what we do, and I live at the beach.
Awful lot of water left on that track. My expertece is null but I'd wait a little bit to panic.
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Remember, we aren't at the season's peak yet.
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1366. pcola57
Quoting JLPR2:
Sunset for Katia.


Pretty Storm.Just wantin' it to stay over water and increase the ACE is all.
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1365. Patrap
Member Since: July 3, 2005 Posts: 414 Comments: 125572
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1363. Patrap
GOM GOES-13 Low Cloud Lee loop
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1362. mrjr101
Quoting notanothergoof:
wasnt katia supposed to be a cat 3 like 2 days ago what happened ?


um, it is not...
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1361. JLPR2
Sunset for Katia.
Member Since: September 4, 2007 Posts: 7 Comments: 8459
Did Katia take a little jog northward in the 5:00 PM update? Sure looks it from my tracking map ---
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Quoting txalwaysprepared:


Still in place over Texas... we have the controls


lol I'd like us to release the controls for just a bit - not for a TS or hurr.. but just a little shower here and there would be a nice start.
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No so sure the GDFL is right about Lee. lol
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Quoting TropicalAnalystwx13:
If Katia follow this track, the storm will be very hard pressed to avoid the United States.


You are right, but of course they'll be criticized if they say that, because of the people who might cancel their travel plans to the beaches.

A lot of folks wait until the kids go back to school, and they relax in September, before the water gets cold.

Heck that's what we do, and I live at the beach.
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Quoting TropicalAnalystwx13:
If Katia follow this track, the storm will be very hard pressed to avoid the United States.


You are right, but of course they'll be criticized if they say that, because of the people who might cancel their travel plans to the beaches.

A lot of folks wait until the kids go back to school, and they relax in September, before the water gets cold.

Heck that's what we do, and I live at the beach.
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Cloud tops have warmed this afternoon, but that's not really unexpected with such a large system at peak heating. It's hard to maintain such a large area of intense cold cloud tops, especially with a weak system. Lee should start firing up more deep convection later this evening into tonight. In fact, it is starting to ignite already in spots.

It appears that there are one or two brave thunderstorms trying to get going near and just west of the center. :-)

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1352. divdog
Quoting Progster:


He will probably never completely evade the dry air which is why its not forecast to be a Cat 3 or 4. However, as soon (or if) convection can encircle the COC, we will probably see a ramp up to Cat 1.
Sounds like a pretty good bit of rain here in the western florida panhandle and a steady breeze but not much else.
Member Since: August 22, 2008 Posts: 0 Comments: 755
I don't know what to make of Lee
He's a huge semicircle
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Quoting MississippiWx:


ADT is over-respected on the blog. Just like you said, I'd rather have actual observations. The pressure at that buoy and some other surrounding ones has been falling pretty fast this afternoon.
Nothing beats in-situ.

BUT, while the satellite presentation has given the weakening impression to most anyone that looks, ADT was steadfastly declaring OFF to the weakening flag. (But, now ON in the last update.)

In the absence of in-situ obs, I apparently think it has more utility than you do (Which is okay.)
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Quoting HoustonTxGal:


Yes dear, just paste the link there and then you should be well on your way to offending others...lol
Roger that Houston ;)
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Good Afternoon.
Some nice double convective bursts in Katia:
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1346. Patrap
Member Since: July 3, 2005 Posts: 414 Comments: 125572
All of the wind map forecasts for each model are showing a wind shift just like a front on days 3-5 through the central and eastern gulf. From hard SSW to NW after the trough.

Strange. Hybrid for sure.

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Quoting notanothergoof:
oops sorry just being honest


I know. I keep hoping one day the answer will be different. :)
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Quoting wunderweatherman123:
so lee is slowly streghthining based on pressure dropping?
For the last couple of hours, at least, yes.

Entering a weakening phase, now? Maybe.
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Quoting SPLbeater:
Katia starting to look a bit better...arc clouds arent coming out furiously as the was a few hours ago,and i beleive Katia has begun to intensify a little
She's sick .... I don't know what is ailing her in terms of this picture, but it's very strange.

Anyone care to explain this curious picture?

What the heck is going on here?

I know there's high shear to her northeast, but what is causing the sinking air, or is this even what it is?

Thanks in advance ...

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1340. SQUAWK
.
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Link

Within the next hour N.O. going to get slammed with some very heavy rain.
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bob said he hopes that it takes the eastern most edge of the cone, not that it will, and i never heard him say anything about labor day being ok, or anything about labor day at all. bob is a good met. and very respected here in nola. he said he didn't really think lee would take a hard right turn the way the models or nhc say it will. geesh! he also said that lee may be close to hurricane strength by monday. he was just pointing out the different tracks it could take, and saying which ones would be better for nola. everything is still as it was hours ago as far as the forcast goes.
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Quoting txalwaysprepared:


Still in place over Texas... we have the controls


Unless it's all part of the plan for crisis? And punishment for Texas remaining one of the few prosperous states w/a Gov that pulls no punches when criticizing the Magic Weather Machine Operator in Chief....
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About JeffMasters

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