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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NEW ORLEANS — A slow-moving system in the Gulf of Mexico strengthened Friday to become a tropical storm,  as the Big Easy and other Gulf cities prepared for up to 20 inches of rain by unclogging storm drains and upping flood defenses.

"Prepare for the worst, let's hope for the best," New Orleans Mayor Mitch Landrieu urged residents as he declared a state of emergency Friday afternoon. The governors of Louisiana and Mississippi also declared emergencies.

The city has closed flood gates and staged rescue boats ahead of what is expected to be "localized flooding" in some areas over the next five days. New Orleans is also hosting 200,000 visitors attending several conventions this weekend.




http://www.msnbc.msn.com/id/44356786/ns/weather/# .TmF4NqN5mK0
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2136. 996tt
Quoting TravisBickle:
Think there wall be anything more than a blown out mess on your side tomorrow?


Probably not. Not much wind though, so be nice if it would kick up a swell overnight. Waist high, choppy mess right now. Better than nothing. A spot over in Pensacola area may be okay if winds pick up tomorrow, but it will be super crowded.
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Quoting P451:


It's one of the stranger looking systems one finds.

WX03 says it's entangled with the ULL.
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2134. Dennis8
Quoting TexasMariner:



This is what bothers me. I really don't have alot of confidence in the models, intensity or guidance wise, at this point regarding this thing.

Main reasoning is its basically a "neutercane" and is currently in a hybrid core state with no dominant coc (rather several smaller surface vortices rotating around each other topped by a large ull).


Have to wait and see on this one.


Very true..good observation
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Quoting Walshy:


+1

UKMET sent Irene in the GOM for how many runs?



many of times i think
Member Since: May 21, 2006 Posts: 5091 Comments: 115125
Quoting Abacosurf:
That March of 92 storm was a gale....in the gulf.


ok,, what is a Gale Storm
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Quoting P451:
Pretty sorry looking wind field aloft. Those higher wind barbs are rain contaminated.







And on the surface.





Hybrid tendencies on satellite. Poor structure. Low winds.


Dont see a single TS force wind sustained anywhere...
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Quoting P451:
Pretty sorry looking wind field aloft. Those higher wind barbs are rain contaminated.







And on the surface.





Hybrid tendencies on satellite. Poor structure. Low winds.


Rain contaminated flight level winds? Thats a new one to me.
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Quoting ackee:
agree watch may be needed for the LEEward THIS WOULD BE QUITE A SHOCK think umket model was the further south
it does look that way on satelite
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Quoting notanothergoof:
no way a gale?


Maybe I should have turned the sarcasm flag on, sorry peeps! It is not a GALE! lol
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do it look like Katia has stalled or too be moveing vary slow
Member Since: May 21, 2006 Posts: 5091 Comments: 115125
2124. Walshy
Quoting Tazmanian:



that would be the 1st if the umket mode was right


+1

UKMET sent Irene in the GOM for how many runs?
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Quoting doorman79:


A gale in the gulf, that would be a first! lol
That March of 92 storm was a gale....in the gulf.
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2121. scCane
Quoting P451:


It's one of the stranger looking systems one finds.

Looks like Allison's twin to me
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2120. Dennis8
Breezy in Houston this evening BUT no rain and on the SE Texas coast and upper Texas coastal waters..appears more so on the NW side of Lee than obs on the north and NE side this evening as the pressure gradient tightens
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Quoting HoustonTxGal:


Was he banned?


That is what I was told... I'm not sure though...
Member Since: September 1, 2008 Posts: 0 Comments: 672
Quoting ackee:
agree watch may be needed for the LEEward THIS WOULD BE QUITE A SHOCK think umket model was the further south



that would be the 1st if the umket mode was right
Member Since: May 21, 2006 Posts: 5091 Comments: 115125
2117. ackee
Quoting Tazmanian:
looks like too me Katia it moveing a little SW
agree watch may be needed for the LEEward THIS WOULD BE QUITE A SHOCK think umket model was the further south
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Quoting reedzone:


Well then Apparently Allison was a gale, she looked very similar to what Lee currently looks like.


Still not a gale!
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2113. scott39
Quoting P451:


I am in agreement.

Looks more like a developing gale than a tropical cyclone.

Does your gut tell you this is going to be stronger than a 65mph TS at landfall. Gut only please, if your wrong no one will care. Lol
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Some people are forgetting that part of the reason Lee looks so dismal is because of the diurnal convective minimum. Dry is a problem too, no doubt.
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2109. CCkid00
Quoting Termite3344:

I am the new guy,, I am in Zachary


just a few miles from me.
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There are ESE winds SW of the LLC at 5,000 feet, not a very well stacked storm... looks more like a nor'easter
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Quoting doorman79:


A gale in the gulf, that would be a first! lol


Well then Apparently Allison was a gale, she looked very similar to what Lee currently looks like.
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looks like too me Katia it moveing a little SW
Member Since: May 21, 2006 Posts: 5091 Comments: 115125
Quoting P451:


I am in agreement.

Looks more like a developing gale than a tropical cyclone.



A gale in the gulf, that would be a first! lol
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Quoting VAbeachhurricanes:
That fix is a full .55 degrees N of the 8pm advisory position, will the NHC come out with a special advisory? because that makes it much closer to land.




it sould dos make it closer too land thats why i think a hurricane watch will go up at some point in time if she comes any march closer
Member Since: May 21, 2006 Posts: 5091 Comments: 115125
Quoting Tazmanian:




or me
where u live taz
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2100. WxLogic
G-IV is almost done with its drops.
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Quoting CCkid00:

I am the new guy,, I am in Zachary
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Quoting MSweatherguy:


Looks nothing like Andrew
didn't say she looked like him.... was asking about the path andrew took, was supost to turn nw and didn't trained west through florida
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That fix is a full .55 degrees N of the 8pm advisory position, will the NHC come out with a special advisory? because that makes it much closer to land.
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Quoting jascott1967:


I find your surfing comments on this message board during hurricane season to be very off-putting and in poor taste.
LMAO
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Quoting MSweatherguy:


The models have been showing for days that it is going to curve out to sea. Not every storm is going to hit Florida

never said it going to hit FL and not every storm is gonna go to the northeast
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Quoting P451:


It's one of the stranger looking systems one finds.




How do you post links
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Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 3rd day of the month at 00:28Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 306)
Storm Number & Year: 13L in 2011
Storm Name: Lee (flight in the North Atlantic basin)
Mission Number: 4
Observation Number: 02
A. Time of Center Fix: 2nd day of the month at 23:57:00Z
B. Center Fix Coordinates: 28°15'N 91°19'W (28.25N 91.3167W)
B. Center Fix Location: 141 miles (227 km) to the SSW (213°) from New Orleans, LA, USA.
C. Minimum Height at Standard Level: 1,430m (4,692ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 31kts (~ 35.7mph)
E. Location of the Estimated Maximum Surface Wind: 14 nautical miles (16 statute miles) to the ENE (66°) of center fix
F. Maximum Flight Level Wind Inbound: From 143° at 39kts (From the SE at ~ 44.9mph)
G. Location of Maximum Flight Level Wind Inbound: 51 nautical miles (59 statute miles) to the NE (54°) of center fix
H. Minimum Sea Level Pressure: 1000mb (29.53 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 14°C (57°F) at a pressure alt. of 1,526m (5,007ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 20°C (68°F) at a pressure alt. of 1,522m (4,993ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 9°C (48°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Wind, Pressure and Temperature
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 7 nautical miles
Remarks Section:
Maximum Flight Level Wind: 39kts (~ 44.9mph) in the northeast quadrant at 23:40:20Z


only TD winds again.
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Quoting Abacosurf:
Yea the ULL has been absorbed. I no longer see it on the NW quad on the Texas coast. It has morphed together.

I know Levi said this was not a hybrid and I know it is warm cored but it is not a "typical" cyclone by any means.



This is what bothers me. I really don't have alot of confidence in the models, intensity or guidance wise, at this point regarding this thing.

Main reasoning is its basically a "neutercane" and is currently in a hybrid core state with no dominant coc (rather several smaller surface vortices rotating around each other topped by a large ull).


Have to wait and see on this one.
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Quoting 996tt:


Yep. I made it over on Thursday and left Sat night. I was in Cocoa Beach area though.
Think there wall be anything more than a blown out mess on your side tomorrow?
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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.