Dr. Jeff Masters' WunderBlog

Tropical Storm Lee moving ashore; Katia continues northwest

Posted by: Dr. Jeff Masters, 1:53 PM GMT on September 03, 2011

+19

Tropical Storm Lee is marching steadily northwards towards landfall in Louisiana, and continues to slowly intensify. The storm's central pressure is now down to 993 mb, as measured by an Air Force hurricane hunter aircraft at 7am CDT. However, the center of Lee is now very close to the coast, and the storm doesn't have much time to intensify further before the center moves over land. The main impact from the storm on the coast thus far has been heavy rains. At New Orleans Lakefront Airport, 5.88" inches of rain had fallen from Lee as of 8 am CDT this morning. Top winds were 35 mph, gusting to 55 mph. Though Lee's top winds are rated as being 60 mph, it is difficult to find any land stations that have reported sustained winds of tropical storm force, 39 mph or greater. One station that has is at the tip of the Mississippi River Delta, where Southwest Pass measured sustained winds of 40 mph, gusting to 58 mph, at 7:03 am CDT. Upper-level winds out of the southwest are creating a moderate 10 - 20 knots of wind shear over Lee, keeping the storm's heavy thunderstorms pushed to the east side of the storm. Latest satelllite loops show Lee is becoming increasingly organized.

Figure 1. Radar-estimated rainfall from Lee from the New Orleans radar. Lee has dumped a large region of 4 - 8 inches so far (orange colors.)

Figure 2. Predicted rainfall for the 5-day period ending at 8 am EDT Thursday Sep 8, 2011. Lee is expected to bring a large swath of 4+ inches of rain all the way to New England. Image credit: NOAA/HPC.

Forecast for Lee
Lee'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 make Lee look a lot like a subtropical storm on satellite imagery, with a broad center and the majority of the heavy thunderstorms in a broad band well removed from the center. Subtropical storms can undergo only relatively modest rates of intensification, and Lee is unlikely to become a hurricane. Also tending to slow intensification will be the fact that much of its circulation is over land. Damages from Lee are likely to be less than $100 - $200 million, with the greatest threats being fresh water flooding from heavy rains. Given that much of the region Lee will traverse over the next few days is under moderate to severe drought, the storm's rains may cause more economic benefit than damage. Since Texas is on the dry side of the storm, that state will see very little rainfall from Lee, except very close to the border with Louisiana. The rains from Lee appear to have mostly ended across extreme southern Louisiana, so the feared 10 - 15 inches of rain does not look like it will materialize there. One possible concern for Lee's rains will be the mid-Atlantic and Northeast, where recovery efforts from the devastating flooding due to Hurricane Irene may be hampered by the additional 2 - 4 inches that may fall from Lee's remnants by the middle of the week.Tornadoes from Lee are potential hazard today, as NOAA's Storm Prediction Center is highlighting the Northern Gulf Coast in their "slight risk" area for severe weather. A tornado watch is posted for the region, but no tornadoes have been reported as of 8 am CDT.

Lee is the 12th named storm this year, and came eight days before the half-way point of the Atlantic hurricane season. Climatologically, September 10 marks the half-way point. A typical hurricane season has just 10 - 11 named storms, so we've already had more than a whole season's worth of storms before reaching the half-way point. At this rate, 2011 will see 24 - 26 named storms, making it the 2nd busiest season on record, behind 2005. Lee's formation date of September 2 puts 2011 in 5th place for earliest date of arrival of the season's 12th storm. Only 2005, 1995, 1936, and 1933 had an earlier 12th storm.

Hurricane Katia
The latest set of model runs show very little change in the outlook for Hurricane Katia. Katia will continue its long trek across the Atlantic Ocean, and will not pose a danger to any land areas over the next five days. Katia is still struggling with dry air and wind shear that has risen to a high 20 - 25 knots. Latest satellite loops show a lopsided hurricane that is suffering from the impacts of dry air and wind shear on its southwest side.

The models now agree that the upper-level trough of low pressure bringing the wind shear to Katia will move away by Sunday, putting Katia in an environment with low to moderate wind shear. At the same time, ocean temperatures will warm to 29°C, a full 0.5°C over what Katia is experiencing today. These effects should allow Katia to intensify to a Category 2 hurricane by Monday. It is still unclear how much of a threat Katia may pose to the U.S., as this depends on the strength and timing of a trough of low pressure predicted to move off the U.S. East Coast 5 - 7 days from now. Our models do not have enough skill to predict how the steering currents will behave that far into the future. As I mentioned in yesterday's post, part of the problem is due to the inability of the computer models to agree on what will happen to Tropical Storm Talas in the Western Pacific. Talas hit Japan early on Saturday as a strong tropical storm, and is racing northwestwards towards Alaska. Talas is expected to transition into a powerful extratropical storm in the waters south of Alaska early next week. This extratropical storm will create a ripple effect downstream in the jet stream, all the way to North America, affecting the trough of low pressure off the U.S. East Coast expected to potentially recurve Katia when it approaches the U.S. The computer models are not very good at handling these sorts of interactions, leading to more than the usual amount of uncertainty in the long-range outlook for Katia. It will probably be another two days before the models will converge on a solution for the long-term fate of Katia. It's a good bet that locations on the U.S. coast south of North Carolina are in the clear, but residents from North Carolina to New England need to watch Katia. Dr. Bob Hart's Historical Tropical Cyclone Probability web page suggests shows that tropical storms in Katia's current position have a 15% chance of hitting North Carolina, a 22% chance of hitting Canada, a 12% chance of hitting New England, and a 58% 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.

Figure 3. Satellite image of Tropical Storm Talas taken September 2, 2011, as the storm approached Japan. Image credit: NASA.

Jeff Masters

So far 4 (minou)

We're in a Lee-lull at the moment but winds have been strong and gusty this morning with blowing rain at times. I had to don my gullashes and wander around the overhang!

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2051. Tazmanian 1:07 AM GMT on September 04, 2011
looks like Katia is moveing a little W Member Since: May 21, 2006 Posts: 5089 Comments: 111624

2052. MiamiHurricanes09 1:07 AM GMT on September 04, 2011
Quoting Tropicsweatherpr: Latest microwave of Katia. Finally got an eyewall to close off. If you look on that same microwave image though, a pocket of dry air lies to the northwest of the circulation (clearly visible on satellite imagery as well). Until it mixes that out, an eye probably won't be visible on satellite. Member Since: September 2, 2009 Posts: 129 Comments: 20002

2053. franck 1:07 AM GMT on September 04, 2011
Quoting HoustonTxGal: Texas= 696200 km2 France=674834 km2 Unfortunately, Texas along same latitude as Libya; France = Nova Scotia. Member Since: August 30, 2005 Posts: 0 Comments: 1150

2055. CaneHunter031472 1:08 AM GMT on September 04, 2011
Jim cantore is in Bay St. Louis Mississippi now, so although the center is of the Coast of LA you can get an idea of where the high winds are. Member Since: August 1, 2007 Posts: 0 Comments: 895

2056. Tazmanian 1:08 AM GMT on September 04, 2011
Quoting P451: Have no put any thought into it. Was so busy watching Lee and sometimes Katia. Never revisited the idea of future storms past those few whacky GFS runs that had several waves developing into storms on Katia's heels. I would suggest the wave that is off of Africa (24) is one of those waves. It doesn't seem to be in a hurry to develop however does it? The other wave further along (22) seems to be in too hostile an environment. ok Member Since: May 21, 2006 Posts: 5089 Comments: 111624

2058. scott39 1:08 AM GMT on September 04, 2011
Quoting beell: The models are keeping with my consistent theme of keeping the surface circulation captured by and rotating around the periphery of the upper low/trough. It was always a possibility I guess. One that I thought was a low probability. 18Z GFS 200mb Valid 18Z Sunday. click Captured and then track where? TIA Member Since: June 13, 2009 Posts: 0 Comments: 6221

2060. franck 1:09 AM GMT on September 04, 2011
Quoting Tazmanian: looks like Katia is moveing a little W Correctamente. Member Since: August 30, 2005 Posts: 0 Comments: 1150

2061. SPLbeater 1:09 AM GMT on September 04, 2011
Katia looks better,i would have 75 back at 11 PM Member Since: August 4, 2011 Posts: 43 Comments: 3961

2062. 5Rockets 1:10 AM GMT on September 04, 2011
Quoting washingtonian115: Soooo what does that mean? Well, here's better info on Katia. It will hit around the N. Carolina/Virginia border, that's what the graphs from NHC, TWC, and Wunderground say. Member Since: August 30, 2011 Posts: 0 Comments: 60

2063. HoustonTxGal 1:11 AM GMT on September 04, 2011
Quoting CosmicEvents: I just checked. Texas is 30% bigger than France! Take that France! And that's just one of our states. . . The full size of France includes it's territories and Islands that it owns. It would be nice if Texas had islands of it's own. They could ship Perry to one. Well, we do have Galveston Island and Padre Island , Dagger Island, Pelican Island to name a few Member Since: September 18, 2007 Posts: 0 Comments: 1038

2064. stormpetrol 1:11 AM GMT on September 04, 2011
Quoting Tazmanian: looks like Katia is moveing a little W Taz, be careful how you say that , you might get labelled a westcaster J/K , how r ya Taz? Member Since: April 29, 2007 Posts: 0 Comments: 6493

2065. ncstorm 1:11 AM GMT on September 04, 2011
12Z EURO ENSEMBLES Katia Member Since: August 19, 2006 Posts: 7 Comments: 8845

2066. Remek 1:13 AM GMT on September 04, 2011
Quoting Matt1989: Models Now, Lee, you follow that GFDL track, y'hear? Good boy! Member Since: August 29, 2005 Posts: 0 Comments: 118

2067. beell 1:14 AM GMT on September 04, 2011
Quoting CosmicEvents: I just checked. Texas is 30% bigger than France! Take that France! And that's just one of our states. . . The full size of France includes it's territories and Islands that it owns. It would be nice if Texas had islands of it's own. They could ship Perry to one. 30% is twice as big, isn't it? To prove that his land is bigger than a Tennessee farm, the Texas rancher bragged, "My ranch is so big that I can get in my pickup and drive all day and all night, and still not leave it!" The Tennessee farmer responded, "I know what you mean. I have an old broke-down truck, too." Member Since: September 11, 2007 Posts: 126 Comments: 13069

2068. will40 1:14 AM GMT on September 04, 2011
Quoting 5Rockets: Well, here's better info on Katia. It will hit around the N. Carolina/Virginia border, that's what the graphs from NHC, TWC, and Wunderground say. there is no graphic from NHC showing it hitting anywhere Member Since: September 19, 2005 Posts: 2 Comments: 3462

2069. Patrap 1:14 AM GMT on September 04, 2011
Member Since: July 3, 2005 Posts: 377 Comments: 112972

2070. 5Rockets 1:14 AM GMT on September 04, 2011
For some reason, I've always assumed Katia and Lee were Irene's top backup. Member Since: August 30, 2011 Posts: 0 Comments: 60

2072. Tazmanian 1:15 AM GMT on September 04, 2011
Quoting stormpetrol: Taz, be careful how you say that , you might get labelled a westcaster J/K , how r ya Taz? doing well Member Since: May 21, 2006 Posts: 5089 Comments: 111624

2076. HoustonTxGal 1:17 AM GMT on September 04, 2011
Quoting beell: 30% is twice as big, isn't it? To prove that his land is bigger than a Tennessee farm, the Texas rancher bragged, "My ranch is so big that I can get in my pickup and drive all day and all night, and still not leave it!" The Tennessee farmer responded, "I know what you mean. I have an old broke-down truck, too." The drive from the east side of Texas to the west side of Texas is about the same distance as driving from Dallas to Chicago. Member Since: September 18, 2007 Posts: 0 Comments: 1038

2077. mamabeth 1:17 AM GMT on September 04, 2011
Looks like Mississippi threw up a shield. All the bands parting and going around it. Member Since: September 11, 2008 Posts: 0 Comments: 9

2079. HuracanTaino 1:17 AM GMT on September 04, 2011
Quoting hurricanehunter27: Eye should pop up tonight or morning but def cat 1. also moving west, west north west, all day, why they say NW? Member Since: May 31, 2011 Posts: 0 Comments: 534

2080. nofailsafe 1:17 AM GMT on September 04, 2011
Went to the store, saw people buying water. I did too, and a case of guinness. For, you know, happy fun rainy time. Member Since: June 18, 2010 Posts: 3 Comments: 852

2081. will40 1:18 AM GMT on September 04, 2011
Quoting 5Rockets: Well, I look at their charts, then I predict where. But I checked yesterday, and there was a chart I just happened to find on NHC. lmao so it is a prediction from you Member Since: September 19, 2005 Posts: 2 Comments: 3462

2083. brazocane 1:18 AM GMT on September 04, 2011
Couple more Lee Sunset pics: Member Since: August 23, 2006 Posts: 0 Comments: 676

2085. ConnecticutWXGuy 1:19 AM GMT on September 04, 2011
Quoting HuracanTaino: also moving west, west north west, all day, why they say NW? because it's actually been moving Northwest. It's just hard to tell on satellite... there's been a lot of wobbles, but when all averaged out the motion is 305 degrees/NW. Member Since: November 17, 2010 Posts: 10 Comments: 521

2086. xtremeweathertracker 1:19 AM GMT on September 04, 2011
New Blog!! Member Since: May 31, 2011 Posts: 57 Comments: 555

2087. NEFLWATCHING 1:20 AM GMT on September 04, 2011
"mamabeth: Looks like Mississippi threw up a shield. All the bands parting and going around it." Well, that pinpoints Cantore. Member Since: September 16, 2008 Posts: 0 Comments: 90

2088. splash3392 1:20 AM GMT on September 04, 2011
Hi Dewey and 5rockets had this same conversation this morning. Nothing significant has changed. Dewey is/was correct! Member Since: January 24, 2007 Posts: 1 Comments: 632

2089. blsealevel 1:20 AM GMT on September 04, 2011
These models all showing lee heading NE and being absorbed by the Atlantic storm But all models also are showing something else starting in the S GOMEX in 3 or 4 days days Member Since: August 23, 2008 Posts: 0 Comments: 1916

2090. PcolaDan 1:20 AM GMT on September 04, 2011
Quoting mamabeth: Looks like Mississippi threw up a shield. All the bands parting and going around it. Must be just your area. See my post 2024 for numbers. Member Since: August 22, 2008 Posts: 12 Comments: 6008

2092. 5Rockets 1:21 AM GMT on September 04, 2011
Quoting will40: lmao so it is a prediction from you Yes. And a good one, too. I mean, not everyone's predictions are perfecto. I'm saying mine's pretty good estimation. Member Since: August 30, 2011 Posts: 0 Comments: 60

2093. A4Guy 1:22 AM GMT on September 04, 2011
NEW BLOG from ANGELA Member Since: June 23, 2006 Posts: 0 Comments: 646

2094. 5Rockets 1:22 AM GMT on September 04, 2011
Quoting 5Rockets: Yes. And a good one, too. I mean, not everyone's predictions are perfecto. I'm saying mine's pretty good estimation. Does anybody object to that? Member Since: August 30, 2011 Posts: 0 Comments: 60

2095. EastTexasWxGal 1:22 AM GMT on September 04, 2011
In East Texas, it has been RAINING steadily for about 4 hours now. Very gentle, soaking rain. This is the most rain we have had in months! Who else in Texas is getting this? This beautiful rain is due to Lee. It looks like it will last another 4 hours or more, but the official forecast says only 30% rain. Member Since: July 28, 2011 Posts: 0 Comments: 3

2096. mamabeth 1:22 AM GMT on September 04, 2011
Quoting PcolaDan: Must be just your area. See my post 2024 for numbers. May very well be. Just looked like it on radar. Know its gonna change. Member Since: September 11, 2008 Posts: 0 Comments: 9

2097. JLPR2 1:22 AM GMT on September 04, 2011
Seems like the only way for Katia to bring at least a band of rain to my area is to move due west for at least a day and that is highly unlikely. I bed adieu to Katia and wish the Bahamas, Bermuda, East Coast and Canada good luck. Member Since: September 4, 2007 Posts: 7 Comments: 7528

2098. 5Rockets 1:23 AM GMT on September 04, 2011
Quoting twincomanche: 5Rockets=Troll?? Nope. Not a troll. Member Since: August 30, 2011 Posts: 0 Comments: 60

2100. Tazmanian 1:23 AM GMT on September 04, 2011
little too no dust in the way wind shear seems low for PG23L and PG24L Member Since: May 21, 2006 Posts: 5089 Comments: 111624

2101. franck 1:25 AM GMT on September 04, 2011
Quoting HoustonTxGal: Heck, many of us down in here in Texas have our CHL..Perry is just more in the spotlight about it. Heck, I have a CHL :o) Oh, you're not telling me..I'm from Alabama. Sold my guns years ago. You know the saying, live by the sword.... Member Since: August 30, 2005 Posts: 0 Comments: 1150

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