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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Member Since: July 14, 2006 Posts: 0 Comments: 1163
686. IKE
72 hour 12Z ECMWF....985 mb's....


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Quoting IKE:

Agree...they have shifted east.


Top O' The Day to ya Ike. Long time no see. Bracing for some wet weather there?
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Member Since: July 3, 2005 Posts: 428 Comments: 129841
Has anyone seen Bahahurican on in the last few days?????

Last post I saw was on the 26th.
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Quoting LightningCharmer:
Just what they need in the mid-Atlantic....more rain.


Hopefully it'll just impact the south, emerge back into the Atlantic and speed out to sea. Hopefully it's not feeling Vermonty.
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12z UKMET Link
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678. 996tt
Quoting TexasHurricane:
Quoting laguna2:


In central Texas we're beyond exasperation. I think depression (in the psychological not meteorological sense) is a good description of my mood too.


Dunno, maybe if you talk about it on every page and beg mother nature, you might get a hurricane or TS. Needs to be every page though as I am sure many and mother nature keeps forgetting.
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677. IKE

Quoting hurricanejunky:
Models shift slightly east...
Agree...they have shifted east.
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676. jpsb
Quoting P451:


Yeah that really stinks. Must be tough having watched all those model runs that had it circling around to Texas and now.... nothing.
I have not yet given up hope that the Texas high at least the eastern part of it erodes enough to let some of Lee get into the Houston Galveston area. Maybe that ULL will do it. I know it's a long shot, but I have my fingers crossed. And then there is always the possiblity of Lee being steered into N. Mexico or S. Texas but I don't like that idea, too much time over open water, and not yet ready to sacrifice Brownsville for drought relief, even thou the idea does have some appeal.
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Quoting hurricanejunky:
Models shift slightly east...
Just what they need in the mid-Atlantic....more rain.
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Models shift slightly east...
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Quoting IKE:
988mb's @ 48 hours...




It's the no see um's that get you........
It clipped my comment:

Speaking of nee see um's I can only imagine what the skeeter population is going to be like in La after this
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Quoting P451:


Will the two cones overlap each other would be a better question.


My concern right now is of course the flooding that could occur in Louisiana. However, if this system should move into the Northeast, it could cause the high to move further to the west. With Katia out there and another possible system developing behind her, it it not a good set-up.
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Quoting Hurlo:


That's a fantasy of mine.


That's a weird fantasy. I have a fantasy that it rains in Texas some day.
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667. gecko
Quoting P451:


It's some sort of a defense/preparation mechanism. Not just perfectly natural but a good instinct.


My friends call it "nesting".
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Quoting BeanTech:
This just in:

Oz is on a chartered cessna en route to intercept Katia and do some reconnaissance. He's equipped with his trusty helmet, a parachute, an inflatable life raft and a week's supply of red bull.

Updates forthcoming....
Forgot the smokes in your liste nécessité vitale.
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Quoting P451:


If they say so...




I think we are getting Storm winds now in Gulf Breeze I think they need to move the warnings further East!!
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Quoting rv1pop:

Quoting flowrida:
What is more expensive plywood or plywood tape?

Read back posts... If you are serious... Otherwise, bye. "Plywood tape" Failed promo idea from mid 70's was plywood with tape to hold it in place. You still need screws to hold the plywood during the storm. Read past posts.


Plywood tape is more expensive because it doesn't work and you will at the least be replacing windows!

Those are more expensive than plywood!
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If this has been addressed sorry. But earlier this week there was a lot of talk about the high breaking down over Texas, it appears now that it is not happening. Would someone please explain why and is it just taking longer than expected or not going to happen at all. I beleive that Levi, mentioned earlier that it was still in place. Also please educate me on what makes a high move, is it an ooutside source or is it the feature itself? Still begging for rain here in Corpus! Thank you for any input.
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if the large comma tail on this thing continues building (like it has for the last 5 hours, up to 180° currently) it will circle all the way around the center and close up just south of Galveston.
Quoting Patrap:
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Frog-strangling rain about an hour ago. Gulf Beach Highway west of Perdido Key. Looks like we'll be getting a lot of the rain that Texas desperatly needs.
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658. IKE
988mb's @ 48 hours...


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AT 100 PM CDT...1800 UTC...THE CENTER OF TROPICAL STORM LEE WAS
LOCATED BY AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT AND
OBSERVATIONS FROM OIL RIGS TO BE NEAR LATITUDE 27.4 NORTH...
LONGITUDE 91.5 WEST. LEE IS DRIFTING TOWARD THE NORTHWEST NEAR 2
MPH...4 KM/H. A CONTINUED SLOW AND POSSIBLY ERRATIC MOTION TOWARD
THE NORTHWEST OR NORTH IS EXPECTED TODAY AND SATURDAY. ON THE
FORECAST TRACK...THE CENTER OF THE TROPICAL STORM IS EXPECTED TO
APPROACH THE COAST OF SOUTHERN LOUISIANA DURING THE WEEKEND.

MAXIMUM SUSTAINED WINDS HAVE INCREASED TO NEAR 40 MPH...65 KM/H...
WITH HIGHER GUSTS. GRADUAL STRENGTHENING IS FORECAST DURING THE
NEXT 48 HOURS. WIND GUSTS TO NEAR 60 MPH ARE BEING REPORTED ON OIL
RIGS NORTH AND EAST OF THE CENTER AT ELEVATIONS OF A FEW HUNDRED
FEET ABOVE THE OCEAN SURFACE.

TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 200 MILES...325
KM...MAINLY NORTHEAST THROUGH SOUTHEAST OF THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE BASED ON REPORTS FROM NEARBY
OIL RIGS AND AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT IS 1003
MB...29.62 INCHES.


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Quoting flowrida:
What is more expensive plywood or plywood tape?
Read back posts... If you are serious... Otherwise, bye. "Plywood tape" Failed promo idea from mid 70's was plywood with tape to hold it in place. You still need screws to hold the plywood during the storm. Read past posts.
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Quoting Hurlo:


or a Heineken


Spaten Optimator.
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Doesn't look like an Invest to be declared soon on the new wave.

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I know I drank too much last night but I swear I just saw Patrick driving a boat? I also see lee is officially here.
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Quoting angiest:


Drop that same earthquake in NYC and the shaking would almost certainly be felt in Kansas City. Alaska is on an active margin (specifically a convergent boundary) and the rocks are so fractured that shaking doesn't carry very far. Remember the area that can feel New Mardrid earthquakes:



BTW, we are approaching the 200th anniversary of those quakes.

Oh, I agree that eastern quakes--overlying solid bedrock as they do--will be felt over relatively large areas when compared to Western quakes of the same magnitude. I was just using the distance comparisons to remind people of Alaska's enormous size. At any rate, powerful as a 35km, 6.8 tremor is, it's not gonna be felt through 1,000 plus miles of Aleutian rock, right?
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Quoting HCW:


A very good chance as soon at 10pm this evening . Hello from the Island :)


Hi from Dawes area of West Mobile! How is the weather on DI right now??
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Quoting jpsb:
Opps, sorry I thought you said Lee might be pushed back into the gulf from a front coming down south, and if it that happened there was a small chance of lee being steered sw into n. Mexico or s. Texas by the high to the west.

Anyway I was just trying to give you credit for the forecasting the apparent move south :) guess my memory needs a little work :(


Lol, well he could try to dance in and out with the coastline for a while, but my forecast yesterday was for a looping track in the NW gulf and then a move into Louisiana. That loop would include some southerly movement, but we'll have to see if we actually get a loop. These wacky tracks are hard to get right, but it's the end-result that counts.
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Looking at the two cones, I wonder if Florida will be in two cones at once soon.
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Quoting cat6band:
Levi...haven't had a chance yet to look at your tropical tidbit yet.... but what are your thoughts on Lee topping out at? Thanks!


60-70mph if landfall occurs on Sunday. If he stays over the gulf waters until Monday then he could reach Cat 1 strength, in my opinion.
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Quoting linkays:


Agreed! Isn't it a shame we have to wish for a storm, even a hurricane, just to get some rain? I hate to even look at the radar's knowing they are getting what could potentially relieve our drought :(.


What is worse is that the amber alert signs between hou and Galv warn about extreme fire conditions from all of the wind on the edge of the storm.
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Quoting VAbeachhurricanes:
Levi, should I be rooting for Katia to move faster or slower?


Faster. That would bump her into the ridge east of Lee sooner, as well as the trough over the eastern seaboard before it has a chance to lift out too much.
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Grand Isle orders mandatory evacuations of RVs, campers; voluntary evacuation for others
Published: Friday, September 02, 2011, 12:22 PM



A state of emergency has been declared in Grand Isle as of noon today, and a mandatory evacuation order has been issued for individuals in camper trailers and recreational vehicles. A voluntary evacuation has been issued for other residents in light of possible flooding on Louisiana 1, and a shelter has been established at the Larose Civic Center.
Mayor David Carmardelle made the announcement after meeting with city officials all morning and watching weather reports. The town, and most of the Louisiana coast, is preparing for tropical depression 13 which is looming in the Gulf of Mexico and expected to drive heavy rains into the state this weekend.
Information on when residents should return to Grand Isle will be released as conditions are evaluated.
Member Since: July 3, 2005 Posts: 428 Comments: 129841
637. IKE
24 hour 12Z ECMWF....


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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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