Gulf of Mexico disturbance 93L a Lousiana flood threat; Katia a hurricane

By: Dr. Jeff Masters , 3:28 PM GMT on September 01, 2011

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Surface winds over the northern Gulf of Mexico are rising, pressures are falling, and heavy thunderstorms are building today thanks to a tropical disturbance (Invest 93L) that is the product of a tropical wave interacting with an upper-level low pressure system. At 8:35 am CDT, winds at the Mississippi Canyon 711 oil rig were south-southeast at 38 mph. This is just 1 mph below 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 30 mph. Long range radar out of Mobile, Alabama shows heavy rain showers building along the northern Gulf Coast, but these rain showers are not organized into spiral bands and show no signs of rotation. Strong upper-level winds out of the west-northwest are creating 30 knots of wind shear over 93L, keeping the storm's heavy thunderstorms disorganized. Strong onshore winds raising tides to 1 - 2 feet above normal are likely along the northern Gulf Coast through the weekend, and coastal flood statements have been issued for the region.


Figure 1. Predicted rainfall for the 5-day period ending at 8am EDT Sep 6, 2011. A large region of rains in excess of 15 inches is expected over Southeast Louisiana. Image credit: NOAA/HPC.


Figure 2. U.S. drought conditions on August 30. The rains from 93L have the potential to bring major drought relief to drought-stricken portions of the coast. Image Credit: U.S. Drought Monitor.

By late tonight, wind shear is expected to drop to the moderate range, below 20 knots, and 93L should begin to organize into a tropical depression. Wind shear is expected to remain moderate, 10 - 20 knots, into Monday. There is some cold, dry air aloft that will retard this process, and I think the earliest we would see a tropical depression is Friday afternoon. NHC is giving 93L a 70% chance of developing into a tropical depression by Saturday morning. All of the major models develop 93L near the Louisiana coast, and show a slow and erratic movement due to weak steering currents. Coastal Louisiana, Mississippi, Alabama, and the extreme western Panhandle of Florida will likely receive very heavy flooding rains beginning this afternoon and intensifying Friday and Saturday. The latest rainfall forecast from NOAA Hydrological Prediction Center (Figure 1) shows that a large area of 15+ inches of rain is expected over Southeast Louisiana. 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. Nevertheless, minor to moderate freshwater flooding is likely from 93L, and 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 (31.3°C), which will provide plenty of moisture for heavy rains, and plenty of energy to help 93L strengthen into a tropical storm. Most of the models predict 93L will have some motion to the west by Saturday, which would bring rains to the Texas coast near the Louisiana border. Steering currents will be weak in the Gulf this weekend and early next week, making it difficult to predict where the storm might go. If 93L stays over water through Tuesday, like the ECMWF model is predicting, the storm would be a threat to intensify into a hurricane. Most of the other models predict 93L will move ashore over Louisiana by Sunday, limiting the storm's development to just tropical storm strength. I think it at least 50% likely 93L will be a tropical storm with 40 - 60 mph winds along the coast of Louisiana by Sunday.

Hurricane Katia
Hurricane Katia intensified into the 2nd hurricane of the 2011 season last night, and continues its long trek across the Atlantic Ocean today. Katia is expected to arrive at a position several hundred miles north of the Northern Lesser Antilles Islands by Monday. The islands are not in the cone of uncertainty, and it appears unlikely that they will receive tropical storm-force winds from Katia. Satellite images show that Katia is a well-organized storm with plenty of heavy thunderstorms, but the storm has been struggling with dry air and moderate wind shear of 10 -20 knots, and is looking less organized than it did last night. These problems will likely diminish by Friday night, as the upper low bringing the wind shear moves away. It is still unclear how much of a threat Katia may post to the U.S. Dr. Bob Hart's Historical Tropical Cyclone Probability web page suggests shows that tropical storms in Katia's current position have an 16% chance of hitting North Carolina, a 21% chance of hitting Canada, a 12% chance of hitting Florida, and a 54% chance of never hitting land. I suspect that Katia will turn north before reaching the U.S. and potentially threaten Bermuda and Canada, based on what past storms in similar situations have done, and assuming the jet stream maintains its current pattern of bringing frequent troughs of low pressure off the coast of the U.S. It will be another day or two before the models will begin to have a handle on the long-term fate of Katia, though.


Figure 3. Morning satellite image of Katia.

94L
A well-organized low pressure system with a surface circulation and limited heavy thunderstorm activity has developed between Bermuda and the Canadian Maritimes. This disturbance, (94L), is headed out to sea, and is being given a 10% chance of developing into a tropical depression by NHC. 94L is under a very high 30 - 40 knots of wind shear, and will not be able to intensify very much. However, Tropical Storm Jose formed from a similar type of system, and we might get surprised by 94L.

I'll have more on Irene in tomorrow's post.

Jeff Masters

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1895. Patrap
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TD#13...somehow...
Member Since: July 7, 2010 Posts: 0 Comments: 5639
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1892. KEEPEROFTHEGATE (Mod)
Tropical.Cyclone.Formation.WARNING
013/TD/L/CX
MARK
25.95N/89.91W


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Not again...
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Quoting Levi32:
NHC track basically stalls TD 13 over LA - could mean flooding rainfall.


I take back my wish all season for a stalled TS. My wish was for one over TX and west central LA, not New Orleans. Geez, the wish fairy could have gotten the right place at least!
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A little rain falling in Orange, Jefferson and Hardin counties of SE Texas. God give us some more, please!
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Quoting Col15thTex:


Not sure where you live, but Texas could use inches of rain NOW. With the extent of the drought a slow soaking rain will not make a dent. We need inches falling on the aquifer recharge zones. I don't think folks realize how serious Texas' plight is. This is far worse than the 1953-56 drought. Springs and creeks have dried up that were still flowing in the '50's.



THANK YOU!!!!
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1886. KEEPEROFTHEGATE (Mod)
T.C.F.A.
012/TS/K/CX
MARK
16.45N/50.15W



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Quoting TropicalAnalystwx13:
The last thing Texas needs right now is 93L/TD #12/Lee, or whatever you want to call it. 93L promises to be a HUGE rain-maker, and torrential rains up to 20" is not good for Texas. It would cause significant flooding, and would probably be as damaging as Tropical Storm Allison (2001).

What Texas needs is several days of LIGHT rain, nothing heavy.


Not sure where you live, but Texas could use inches of rain NOW. With the extent of the drought a slow soaking rain will not make a dent. We need inches falling on the aquifer recharge zones. I don't think folks realize how serious Texas' plight is. This is far worse than the 1953-56 drought. Springs and creeks have dried up that were still flowing in the '50's.

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Quoting P451:


Well, that's the reasoning behind the early declaration. But to do so they have to ignore their own checklists for what passes as a tropical cyclone. Well, their choice.


26.6 91.4 huh. Well, that'd be this:




lol.

Damn. Must be subtropical lol.

(Yes, I understand why the circulation is displaced to the west of the convective activity).
Member Since: September 2, 2009 Posts: 130 Comments: 21091
1882. mig123
is Katia taking andrews path ??
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Quoting aislinnpaps:
Patrap, your images make it look so much bigger.

They just announced her TD 13 officially.
that's what she .....ahh...forget it.
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1880. Patrap
Orleans
Coastal Flood Watch, Flash Flood Watch
Statement as of 3:12 PM CDT on September 01, 2011

... Coastal Flood Watch now in effect through Sunday evening...

The coastal Flood Watch is now in effect through Sunday evening.

* Coastal flooding: tides are currently running 1 to 2 feet
above normal this morning. Tides are expected to continue to
rise to 2 to 3 feet above normal. Tides are expected to be
highest in areas bordering Lake Borgne and along the Hancock
County Mississippi coast. Tides could be significanly higher
if the surface low becomes stronger than currently expected or
is much closer to the region.

* Timing: the highest tides are expected to begin Friday and
last through the weekend.

* Impacts: the high tide levels may produce flooding in low
lying areas outside of hurricane protection levees in
southeast Louisiana and in low lying areas along the
Mississippi coast and Lake Pontchartrain. This will cause
inundation of mostly secondary roadways. These higher tide
levels will also inhibit drainage of area rivers.

Precautionary/preparedness actions...

A coastal Flood Watch means that conditions favorable for
flooding are expected to develop. Coastal residents should be
alert for later statements or warnings... and take action to
protect property.






310 PM CDT Thu Sep 1 2011

... Flash Flood Watch remains in effect through Sunday evening...

The Flash Flood Watch continues for

* portions of southeast Louisiana and southern Mississippi...
including the following areas... in southeast Louisiana...
Assumption... lower Jefferson... lower Lafourche... lower
Plaquemines... lower St. Bernard... lower Terrebonne...
Orleans... St. Charles... St. James... St. John The Baptist...
upper Jefferson... upper Lafourche... upper Plaquemines... upper
St. Bernard and upper Terrebonne. In southern Mississippi...
Hancock... Harrison and Jackson.

* Through Sunday evening

* efficient and torrential tropical rains will continue to impact
coastal Mississippi and southeast Louisiana through the Labor
Day weekend. Rain rates of 1 to 3 inches per hour can result in
flash flooding and general ponding of water in streets. Model
estimates and the NOAA Hydrometeorological Prediction Center
indicates an average of 10 inches may occur this weekend across
the watch area. Localized higher amounts 15 to 20 inches are
possible... depending on future developments of the Gulf system
into early next week.

Precautionary/preparedness actions...

Residents and businesses in the watch area should ensure that
drainage ditches... catch basins... and culverts are cleared of
debris before rains onset to allow for adequate drainage.

A Flash Flood Watch means that conditions may develop that lead
to flash flooding. Flash flooding is a very dangerous situation.

You should monitor later forecasts and be prepared to take action
should flash flood warnings be issued throughout the weekend.
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Quoting Patrap:



What most never understand,itsa da water, not the Wind.
For most...

Up here in the piney woods, a.k.a. the hills, wind more of a problem.
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Quoting Patrap:



What most never understand,itsa da water, not the Wind.


Hey, there goes your marsh fire, Pat...
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plenty of "what-if casting" going on here tonight.
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Quoting notanothergoof:
we are getting prepared here in florida gonna hit walmart and home depot tommorow early before the crows get there

For what 2012?
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Quoting Seflhurricane:
hey miami i am starting to believe that Katia is not going to head North west as the models indicate, and i have noticed with every run a further west trend , does it looks like the northern islands are in danger


I fear that Katia will affect the OBX and SE Virginia where Irene just passed through. What Irene gave us as a body blow, Katia could finish off with a right hook.
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1873. hahaguy
TD 13's cone looks like a backwards apostrophe.
Member Since: August 12, 2007 Posts: 2 Comments: 2838
Quoting Levi32:
I hope Pre Lee doesn't become no Alison part two....she just wouldn't stop causing problems.
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Quoting Levi32:
Fay's mirror...
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1870. aquak9
Quoting notanothergoof:
oh no does that mean florida again?

(loads BB gun with Valium)
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Just saw td 13 on navy site
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Quoting TropicalAnalystwx13:
They might have called TD just so they could post TS warnings.

Though, I think I would have called a TD based on HH obs, myself.
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Quoting Levi32:
NHC track basically stalls TD 13 over LA - could mean flooding rainfall.


Considering how the NHC said they are most in line with the Euro/GFS track, it could stick around over water another day or two. The GFS moves it inland faster, but the Euro keeps it over water a day or so longer. It will be interesting to see which one occurs as another day could mean the difference in a moderate strength tropical storm and a high end Cat 1 hurricane.
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1865. Patrap
26C GOM Thermocline

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1863. DFWjc
Quoting Dakster:


Not likely, one will overpower and absorb the other.. Worst case is a fujiwara affect... (I hate to use that word here as I am sure I will get flamed for it)

But that is rare.. Usually one just steals the mojo from the other.


Here's some examples:
A few sets of examples can be found in the busy 1995 Atlantic hurricane season. During the height of the season, Hurricane Humberto and Hurricane Iris took part in a brief Fujiwara interaction. Iris then began interacting with a third storm, Tropical Storm Karen, which orbited and later merged with the more intense Iris.

In 2004, Lisa absorbed a tropical disturbance as described in the Tropical Cyclone Report.

In 2005, the remnant low of Tropical Depression Thirteen moved northward and then northeastward around a non-tropical low located to the north of the system. It briefly strengthened into Tropical Storm Lee. Thereafter, Lee weakened back to a tropical depression as it moved northeastward and northwestward around the eastern side of the non-tropical low and eventually absorbed the non-tropical low.

In the same year, Alpha was absorbed by Wilma.
Member Since: July 19, 2011 Posts: 1 Comments: 1006
Cute lil' bubble cone.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
1861. tj175
I agree
Quoting Clearwater1:
Main article: Meteorological history of Hurricane, para phrased from Wikapedia


A tropical wave moved off the coast of Africa on August 14. Under the influence of a ridge of high pressure to its north, the wave tracked quickly westward, developing into a Tropical Depression late on August 16 about 1,630 mi (2,620 km) east-southeast of Barbados. By August 17, the depression intensified into a Tropical Storm , and by the following day had organized convection and estimated winds of 50 mph (80 km/h). Shortly thereafter the thunderstorms decreased markedly,[3] and as the storm turned to the northwest it encountered southwesterly wind shear from an upper-level low. On August 19, a Hurricane Hunters flight into the storm failed to locate a well-defined center, and the next day a flight found only a broad circulation with an unusually high pressure of 1,015 mb (30.0 inHg). Around that time, the upper-level low degenerated into a trough, which decreased the wind shear over the storm. In addition, a strong ridge developed over the southeastern United States, which built eastward and caused Andrew to turn to the west.


This of course is a report on Andrew, but change the dates a bit and it reads all to similar to some of the more recent reports about Katia, or what you may be reading at eleven pm and 5 am
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LOL...Two circles!

Member Since: July 6, 2010 Posts: 113 Comments: 31564
-
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1858. Levi32
Member Since: November 24, 2005 Posts: 635 Comments: 26566
Quoting CybrTeddy:


TD 13 looks like a moderate Category 2 hurricane compared to No way Jose.
Jose just went missing in the Atlantic.Lol.
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1856. Patrap



What most never understand,itsa da water, not the Wind.
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Quoting atmosweather:


All necessary conditions have been met for tropical cyclone formation. Warm core, a closed LLC (weak I know), persistent convection over or near the LLC for 12 hours or more (not a great deal but just enough), sustained winds of at least 30 mph measured by RECON instruments or observations from the ground.


I don't get why the TPC is so hellbent on naming storms that aren't warm core storms, like Jose (and no threat to land). Is it to pump up their numbers for some political agenda (man made global warming)?
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Yup. It's September.
Member Since: July 7, 2010 Posts: 0 Comments: 5639
1852. Dakster
Patrap - Looks like you are going to get blown soon...

By TD13...
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Member Since: July 6, 2010 Posts: 113 Comments: 31564
1850. drj27
hopefully we are good here in the fla panhandle
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Quoting JGreco:


Are these two storms having or going to have a influence on each other. I've been shocked by the models so far...I really don't know what to expect from either:o


Very unlikely unless TD 13 stays in or around the Gulf of Mexico for a really long period of time. I favor a quicker landfall time than many of the models have been calling for (3 days at most compared to 5 days).
Member Since: September 24, 2005 Posts: 33 Comments: 9265
1848. Patrap
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1847. Dakster
Quoting notanothergoof:
can katia and newly declared 93l come together to form the perfect storm?


Not likely, one will overpower and absorb the other.. Worst case is a fujiwara affect... (I hate to use that word here as I am sure I will get flamed for it)

But that is rare.. Usually one just steals the mojo from the other.
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1846. Levi32
NHC track basically stalls TD 13 over LA - could mean flooding rainfall.
Member Since: November 24, 2005 Posts: 635 Comments: 26566
Quoting washingtonian115:
No offense....but T.D 13 has got to be one of the ugliest T.D's I have seen.


TD 13 looks like a moderate Category 2 hurricane compared to No way Jose.
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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.