Flash Floods Kill 3 in Colorado; Dangerous 93L Developing in Gulf of Mexico

By: Dr. Jeff Masters , 3:06 PM GMT on September 12, 2013

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Devastating flash floods swept though numerous canyons along the Front Range of Colorado's Rocky Mountains Wednesday night and Thursday morning, washing out roads, collapsing houses, and killing at least two people. The floods were triggered by widespread torrential rains of 4 - 6" that fell in less than twelve hours, thanks to a flow of extremely moist air from the southeast that pushed up against the mountains. These sort of upslope rain events are so-named because as the air flows uphill, it expands and cools, forcing the moisture in it to fall as rain. Balloon soundings from Denver last night and this morning recorded the highest levels of September moisture on record for the station. The total precipitable water (PW), which is how much water would fall at the ground if the entire amount of water vapor through the depth of the atmosphere was condensed, was 1.33" at 12Z (8 am EDT) on September 12, and 1.31" at 00Z September 12. The previous September record was 1.23", set on September 10, 1980. Balloon soundings began in 1948. Wednesday night's rainfall was heaviest near Boulder, Colorado, where a flash flood watch continues through Thursday evening. Though rainfall amounts today are not expected to be as great as on Wednesday, the soils are saturated, and additional flash flooding will occur today as an upper-level low centered over the southern Great Basin continues to pull a moist southeasterly surface flow of air across Eastern Colorado. A map of Boulder flood zones and detailed history of previous floods in the area may be found here.


Figure 1. Flooding in Boulder, Colorado on Wednesday evening, September 11, 2013. Photo posted by brandish on Instagram @photogjake.


Figure 2. Radar-estimated rainfall for the Colorado's Front Range from the September 11 - 12 flash flood event. Rainfall amounts of 6 - 8" (dark rad colors) were indicated near Boulder (circle with a "+" symbol), and confirmed by rain gauge measurements.


Video 1. Flooding in Boulder, Colorado at 36th and Colorado Street on Wednesday night, September 11, 2013.

Dangerous 93L developing in the Gulf of Mexico
A low pressure system (Invest 93L) over the Southwestern Gulf of Mexico's Bay of Campeche is generating heavy rains over the Yucatan Peninsula and adjacent waters as it moves west-northwest at about 5 mph. Radar loops from Mexico show that 93L has a pronounced rotation and is developing low-level spiral bands, and there is a strong possibility that the Air Force hurricane hunter plane scheduled to investigate 93L Thursday afternoon will find that a tropical depression has formed. Satellite loops show only a modest area of heavy thunderstorms, but these are steadily growing in intensity and areal coverage. The atmosphere is unusually moist, ocean temperatures are a very warm 29 - 29.5°C (84 - 85°F), and wind shear is a moderate 10 - 15 knots. These favorable conditions for development are expected to continue through Monday, according to the latest SHIPS model forecast. The computer models predict a landfall location along the Mexican coast between Veracruz and a location a few hundred miles south of the Texas/Mexico border by early next week. The storm is expected to maintain a forward speed of about 5 mph during the coming five days, and this slow motion will potentially allow 93L enough time to intensify into a hurricane before landfall. The high levels of moisture and slow motion of 93L make it a very dangerous rainfall threat, and I expect rainfall amounts of 5 - 10 inches will affect portions of the Mexican coast between Veracruz and Brownsville, Texas over the next five days. An added danger is the presence of tropical disturbance 90E in the Eastern Pacific Ocean, on the other side of Mexico. If 93L intensifies sufficiently, it could draw in the moisture from 90E across Southern Mexico, resulting in torrential rains on both the Pacific and Atlantic sides of Southern Mexico. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave 2-day odds of development of 60% and 5-day odds of 80%.


Figure 3. Latest satellite image of Tropical Depression Ten.

Humberto peaks in intensity
Hurricane Humberto is headed northwards over the far Eastern Atlantic, and has likely peaked in strength, with 85 mph winds. Humberto is listed in NHC's preliminary Best-Track data repository as having achieved hurricane strength at 8 am EDT on September 11, which would tie it with Hurricane Gustav of 2002 for latest appearance of the season's first hurricane since 1941. Satellite loops show that Humberto is well-organized hurricane with a distinct eye, but the storm has moved over waters cooler than 26°C, and wind shear has risen to 20 knots, which will likely cause weakening over the next few days. Humberto is not expected to be a threat to any land areas.

Gabrielle heads towards Canada
Tropical Storm Gabrielle is headed northwards to Canada after bringing 40 mph winds and just over an inch of rain to Bermuda on Tuesday night. Satellite loops show that wind shear has ripped up Gabrielle, leaving the storm with almost no heavy thunderstorms, and exposing the low level circulation to view. Wind shear is expected to rise to an extremely high 45 - 70 knots on Friday as Gabrielle encounters a trough of low pressure, which will likely destroy the storm. Gabrielle's remnants will likely bring heavy rain to the Canadian Maritime Provinces on Friday and Saturday.

Jeff Masters

After the Rain (mtnwoman67)
Lots of rain in Colorado for weeks. Last evening's setting sun gave us a great show east of us.
After the Rain

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It looks as if one thing that will prevent 10L from significantly strengthening is sheer.






24hours


72 hours
Member Since: June 25, 2011 Posts: 2 Comments: 3733
Quoting 996. SuperStorm093:
Back from the ban yes.

How long was the ban?
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Member Since: July 3, 2005 Posts: 426 Comments: 128875
Quoting 990. FunnelVortex:


So you're back.

Just try not to cause trouble this time.
Back from the ban yes.
Member Since: Posts: Comments:
Quoting 993. FunnelVortex:


It'll have a lot of time, so it doesn't really matter.

Okay thanks.
Member Since: September 11, 2013 Posts: 0 Comments: 84
Quoting 945. CaneHunter031472:
Another meteorological freak. What a failure. Ugh I can't wait for this season to be over. I can't wait for winter to come.

Nothing is ever normal in meteorological. Accept that and you'll enjoy it :)
Member Since: August 1, 2011 Posts: 28 Comments: 8032
Quoting 988. Stormlover16:
Since 10L is a very large system, won't it take a lot longer to spin up than Barry and Fernand?


It'll have a lot of time, so it doesn't really matter.
Member Since: October 20, 2012 Posts: 7 Comments: 2873
Boulder Creek continues to rise:

10:55am


4:39pm

(Click image for live cam)

And for those tempted to say these webcam stills make Boulder Creek look relatively placid, please note this is what it looks like about 6 blocks upstream... (yes, really)

Member Since: March 26, 2006 Posts: 44 Comments: 1520
Quoting 968. HurricaneCamille:


Which is why I said it's ORGANIZING.

And alright, no need to get snippy.
Member Since: September 11, 2013 Posts: 0 Comments: 84
Quoting 984. SuperStorm093:
Just want to say my prayers are going out for the people affected by the fires down the shore. They can't catch a break.


So you're back.

Just try not to cause trouble this time.
Member Since: October 20, 2012 Posts: 7 Comments: 2873
WOW!!! 9 Inches rain predicted for me! :o
Member Since: Posts: Comments:
Since 10L is a very large system, won't it take a lot longer to spin up than Barry and Fernand?
Member Since: September 11, 2013 Posts: 0 Comments: 84
This is the GRLevel3 estimate of rain total since the event had begun. Boulder is located in 8+ inches area (pink) with a spot of 10 to 11 inches (purple spot to SE of Boulder). Lot of rain over there.

Member Since: August 1, 2011 Posts: 28 Comments: 8032
I used to live in Colorado Springs when I was a kid before moving to NC. I went out there in April of 2012 for vacation before the huge fires and now this flooding. Watching all the same areas I got to enjoy being burned and washed away is very sad to see. Makes me even more thankful I went when I did.
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985. beell

Current EPAC Surface Analysis
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Just want to say my prayers are going out for the people affected by the fires down the shore. They can't catch a break.
Member Since: Posts: Comments:

Member Since: July 3, 2005 Posts: 426 Comments: 128875
982. beell
The full-blown monsoon through a deep layer-spanning the EPAC and ATL basins as depicted in the 300-850 mb CIMSS steering. If viewed as a singular system, not a lot of "steering".

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Quoting 976. nofailsafe:


The totals further up the coast and inland aren't anything to sneeze at either.
While some will get too much, I'm afraid the Texas totals are over blown. We've seen this too many times, we need a more direct hit. But I keep my hopes up.
Member Since: August 10, 2007 Posts: 0 Comments: 3289
I also look forward to seeing the Mean Spread from the 18z run since it looks like the GFS operational is prognosticating a strike further up the coast.
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Member Since: July 3, 2005 Posts: 426 Comments: 128875
Quoting 975. Doppler22:

Thats alot of rain... and that even sends quite a bit to S. Texas. Wow. My thoughts go to Mexico as this could be a very bad storm


It could be Colorado x1000
Member Since: October 20, 2012 Posts: 7 Comments: 2873
Quoting 933. MrMixon:


I'm glad to see you on here. Am I remembering correctly that you are in the Nederland area? I read early today that one death was reported there, and was wondering how bad you had it there.
Member Since: Posts: Comments:
Quoting 975. Doppler22:

Thats alot of rain... and that even sends quite a bit to S. Texas. Wow. My thoughts go to Mexico as this could be a very bad storm


The totals further up the coast and inland aren't anything to sneeze at either.
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Quoting 964. nofailsafe:
The ptot up to 177 hours is pretty impressive...


Thats alot of rain... and that even sends quite a bit to S. Texas. Wow. My thoughts go to Mexico as this could be a very bad storm
Member Since: February 13, 2012 Posts: 11 Comments: 3783
Quoting 971. SLU:
Very impressive for a storm over sub-26 degree water. There's much warmer water further south but we can't get anything going down there so that highlights that there is a serious suppressive force acting across the TATL this season.



The ULL shearing it.
Member Since: October 20, 2012 Posts: 7 Comments: 2873
Getting some sheer should keep it check.
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Funtown is sad town. I feel for them, too much to bare post Sandy.
Member Since: August 10, 2007 Posts: 0 Comments: 3289
971. SLU
Very impressive for a storm over sub-26 degree water. There's much warmer water further south but we can't get anything going down there so that highlights that there is a serious suppressive force acting across the TATL this season.

Member Since: July 13, 2006 Posts: 13 Comments: 5282
Lets just hope the rain doesn't cause too many problems and at least some of it can make its way into Texas to help out the drought there.
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Quoting 967. Mexicanguy:


Thanks.. the central east coast is the most vulnerable due to orographics(sierra madre oriental),flash flooding and muslides are very posible :(


And we are seeing what is going on in with flooding and rain a mountainous region (Colorado).
Member Since: October 20, 2012 Posts: 7 Comments: 2873
Quoting 965. Stormlover16:

I disagree. It still hasn't established a persistent area of convection over the center.


Which is why I said it's ORGANIZING.
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Quoting 959. Birthmark:

Yep. Best wishes to the people of Mexico. Stay safe, neighbors!


Thanks.. the central east coast is the most vulnerable due to orographics(sierra madre oriental),flash flooding and muslides are very posible :(
Member Since: September 17, 2010 Posts: 0 Comments: 9
Quoting 958. TheGreatHodag:


that's what concerns me as well. Also, Joe Bastardi is expecting a Cat 2/3 from td 10 a little north of Tampico bringing devastating rains to Monterrey. Though, of course, this is Joe Bastardi.


Joe is generally a good forecaster, his word can not be dismissed, we should consider it.
Member Since: October 20, 2012 Posts: 7 Comments: 2873
Quoting 960. HurricaneCamille:
looks to be developing banding features.

Looks like it's organizing at a decent rate now

I disagree. It still hasn't established a persistent area of convection over the center.
Member Since: September 11, 2013 Posts: 0 Comments: 84
The ptot up to 177 hours is pretty impressive...

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The ULL seems to be making a perfect exit for future Ingrid and helping it exhale. The more I look the more I'm surprised not forecasting Hurricane.
Member Since: August 10, 2007 Posts: 0 Comments: 3289
Quoting 953. Stormlover16:

Yes, I believe Opal in 1995 did.


I remember Roxane in the same year...Crazy path
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Quoting 954. MAweatherboy1:
2-3 days over water in the BOC is plenty of time for this to make a run at hurricane status, as long as upwelling doesn't get too involved. The NHC forecast looks very reasonable based off of guidance but they may have under forecast the intensity.

looks to be a TS INGRID NOW.
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looks to be developing banding features.

Looks like it's organizing at a decent rate now
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Quoting 934. SLU:
While this may not be an impressive high ACE storm, the potential for it to dump extreme levels of rain in Mexico could make it just as dangerous.

Could be the "storm of the year"

The curse of the "I" storm lives.




Yep. Best wishes to the people of Mexico. Stay safe, neighbors!
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Quoting 950. GatorWX:
Beginning to remind me of Stan. Hate to see it as a cane with all that moisture.



that's what concerns me as well. Also, Joe Bastardi is expecting a Cat 2/3 from td 10 a little north of Tampico bringing devastating rains to Monterrey. Though, of course, this is Joe Bastardi.
Member Since: Posts: Comments:
If you miss a storm it can actually dry you out instead of giving you an increase in rain chances. The most unreliable rain chances are those tied to tropical system.
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Member Since: July 3, 2005 Posts: 426 Comments: 128875
I wouldn't rule out a Brownsville landfall, especially if the movement is slowed and the storm strengthens more than forecasted.

Member Since: June 30, 2013 Posts: 12 Comments: 8578
2-3 days over water in the BOC is plenty of time for this to make a run at hurricane status, as long as upwelling doesn't get too involved. The NHC forecast looks very reasonable based off of guidance but they may have under forecast the intensity.

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Quoting 951. tater5500:
I'm asking because I have no clue, but have their been storms in the past that have sat in the BOC for as long as this one is scheduled to?

Yes, I believe Opal in 1995 did.
Member Since: September 11, 2013 Posts: 0 Comments: 84
Quoting 947. CaneHunter031472:


Welcome to the blog.

Thanks!
Member Since: September 11, 2013 Posts: 0 Comments: 84
951. tater5500
10:18 PM GMT on September 12, 2013
I'm asking because I have no clue, but have their been storms in the past that have sat in the BOC for as long as this one is scheduled to?
Member Since: August 27, 2012 Posts: 0 Comments: 47
950. GatorWX
10:18 PM GMT on September 12, 2013
Beginning to remind me of Stan. Hate to see it as a cane with all that moisture.

Member Since: January 1, 2008 Posts: 0 Comments: 3602
949. HurrikanEB
10:17 PM GMT on September 12, 2013
Quoting 892. stormwatcherCI:
Odds are it will. In the past 5 years the I storm was a hurricane. In the past 15 years only 1 I storm WAS NOT a hurricane.


Granted that that one storm was Ingrid. And the first time the name was used in the Atlantic... could be that she just doesn't want to ever be a hurricane ;)

Edit:
Aside from Ingrid in 2007, and excluding the couple of years where there were less than 9 named storms, the last time that the "I" storm actually failed to become a hurricane was in 1989 with Tropical Storm Iris.
Member Since: May 2, 2008 Posts: 12 Comments: 1340

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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.