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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Guess the second vorticy doesn't matter. 10L it is. ;P
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Quoting 790. CybrTeddy:
Could get a late special advisory, we'll see.

The TWO wasn't issued yet...may still be writing it
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There it is, TD #10. Expect a special advisory at 530pm.
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Recon does indeed show a second closed low in association with TD10. The wind core is associated with the one they investigated first though.

Member Since: July 6, 2010 Posts: 113 Comments: 32802
invest_RENUMBER_al932013_al102013.ren

AL, 10, 2013091218, , BEST, 0, 197N, 937W, 30, 1005, TD, 0, , 0, 0, 0, 0, 1009, 180, 120, 40, 0, L, 0, , 0, 0, INVEST, S
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Quoting 79. CaribBoy:


Lol I would rather say "the rain he deserves" XD XD

I pray for it!
20 inches please!
Member Since: August 19, 2009 Posts: 0 Comments: 139
Quoting 788. Bluestorm5:
Today's announcement is a historic moment for humans, IMO. Voyager 1 leaving solar system after 35 years and becoming 1st manmade object to do so is mindblowning considering it got 100,000 times less computer power than our iPhones does. I'm sure CybrTeddy is very excited about it today :)


The sad thing is that it still use AOL dial up to phone home ;)
Member Since: June 25, 2011 Posts: 2 Comments: 3733
Quoting 787. Mexicanguy:


Interesting how 93-L is feeding with all that moisture from the Pacific


That is why they are forecasting up to 1 meter of rain for the mountain regions. Stay safe.
Member Since: June 25, 2011 Posts: 2 Comments: 3733
Whole bunch of west winds within the vorticy to the west.

203930 1938N 09340W 9625 00363 0031 233 230 291002 003 002 006 03
204000 1937N 09341W 9627 00361 0031 235 231 313002 003 002 003 03
204030 1936N 09342W 9628 00361 0032 234 228 282003 003 001 004 03
204100 1935N 09344W 9625 00364 0033 235 222 282004 004 000 002 03
204130 1934N 09345W 9630 00360 0033 235 219 280005 005 002 002 03
204200 1933N 09346W 9625 00365 0032 236 218 294006 006 002 003 06

They just started ascending again though?
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Could get a late special advisory, we'll see.
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Quoting 771. MiamiHurricanes09:
The pressure instrument is fine...shows a gradual pressure decrease from 1004-1003mb along the data set. 93L's core just isn't that organized.


Ok! The broad nature of the system is expected being its quite large but if it uses the BOC it can ramp up pretty quickly as you said.
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Today's announcement is a historic moment for humans, IMO. Voyager 1 leaving solar system after 35 years and becoming 1st manmade object to do so is mindblowning considering it got 100,000 times less computer power than our iPhones does. I'm sure CybrTeddy is very excited about it today :)
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Quoting 686. GetReal:


After closely watching the LLC on this loop, it appears to me that the LLC has put on the brakes, and is nearly stationary. The illusion of movement to the west is actually the convection wrapping around the west side of the system, and expanding coverage.


Interesting how 93-L is feeding with all that moisture from the Pacific
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They are so lucky in Colorado: 6 inches of rain, WOW!
RAIN, That's what we want in the northern leewards islands. And to be egoist, that's what we want in St Barth's!
So long time without good and heavy rain!
I don't understand why, again, 98L is gone....in the south!
They don't need in Martinique !
WE NEED RAIN HERE !
Member Since: August 19, 2009 Posts: 0 Comments: 139
Time: 20:39:00Z
Coordinates: 19.65N 93.65W
Acft. Static Air Press: 962.4 mb (~ 28.42 inHg)
Acft. Geopotential Hgt: 363 meters (~ 1,191 feet)
Extrap. Sfc. Press: 1003.1 mb (~ 29.62 inHg)D-value: -
Flt. Lvl. Wind (30s): From 290° at 2 knots (From the WNW at ~ 2.3 mph)
Air Temp: 23.3°C (~ 73.9°F)
Dew Pt: 23.1°C (~ 73.6°F)
Peak (10s) Flt. Lvl. Wind: 3 knots (~ 3.4 mph)
SFMR Peak (10s) Sfc. Wind: 11 knots (~ 12.6 mph)
SFMR Rain Rate: 8 mm/hr (~ 0.31 in/hr)
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Looks like 1004.1 now.

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Quoting 768. TropicalAnalystwx13:

I'm not seeing what you're seeing. Looks like one small but closed low-level circulation?

I guess we could wait for an extra pass to receive full confirmation. The area that they're investigating right now with a 1003mb pressure and light winds could very well be an additional vorticy to the west of the original one that they investigated with a pressure of 1004mb.
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Quoting SLU:


"Relatively tight" might be a little on the generous side ...




Better view

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Quoting 764. MiamiHurricanes09:
Kind of reminds me of Alex from 2010. Once it organized its core structure, it may really take off.


All season all I've heard about how "once ___ happens this one should really start to get going"

The storms this season have been absolutely pathetic save Humberto. I'll believe it when I see it.
Member Since: September 6, 2012 Posts: 0 Comments: 304
18z NAM at 72 hours. Backed off big time. Last run had a much stonger storm making landfall further north.
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Quoting 753. Birthmark:

For every person in America that watches Fox there are roughly 99 that do not.

Do the math.
I did the math and I was referring to those that watch cable news. FOX has an audience larger than every other cable news outlet combined. Even those that infer they detest FOX can name every anchor. Why is that? They hate it but still watch it? Why? So they can come on a blog and poo-poo it for fun? It's an interesting human behavior quirk...
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Quoting 763. MrMixon:


Thanks. It really has been a year of extremes around here. As I posted above, the latest tragedy is the cancellation of a significant beer-related event...


fire - check
flood - check
beer festival - what? canceled?
OMG, it is the end of the world!

I feel for ya. :D
Member Since: June 25, 2011 Posts: 2 Comments: 3733
Quoting 764. MiamiHurricanes09:
Kind of reminds me of Alex from 2010. Once it organized its core structure, it may really take off.


Not seeing much in the way of other vorticies, so far everything tells me there's one surface low that's rather broad for now.
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775. SLU
Quoting 761. CybrTeddy:


Which is strange, ASCAT showed a relatively tight low pressure area. Doesn't look like the NHC will upgrade it to 10L for now.


"Relatively tight" might be a little on the generous side ...


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Quoting 768. TropicalAnalystwx13:

I'm not seeing what you're seeing. Looks like one small but closed low-level circulation?



2 TDs! Jk :/
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Quoting 765. Hurricanes305:


Really? I don't have access to detailed Recon assessment but that pressure might be contaminated.
Contaminated? Call EPA now.
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re: 707. MrMixon 3:19 PM CDT on September 12, 2013
Quoting MrMixon:
An intersection in Longmont, Colorado as it normally looks, and as it looked earlier today:



Again, thanks for your steady updates and images, Mr Mixon... Sheesh, ULL to your west, stalled boundary overhead, results about same as looked here with TS Allison '01 or Hurricane Juan '85 - I recorded over 16" in two days with latter... and close to 21" in 4 days with Allison (near 30" recorded 15 miles above me in Thibodaux LA)...

Sympathies and best wishes to you and all our friends there.

Work calls, check back later...
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Quoting 765. Hurricanes305:


Really? I don't have access to detailed Recon assessment but that pressure might be contaminated.
The pressure instrument is fine...shows a gradual pressure decrease from 1004-1003mb along the data set. 93L's core just isn't that organized.
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Quoting 760. HadesGodWyvern:




already occurring as tropical cyclone Man-yi


Thanks! You're the specialist on this part of the world in this blog :)
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Quoting 756. MiamiHurricanes09:
Pressure down to 1003.1mb now. Looks like 93L is actually a lot more disorganized than previously thought. Could be a large area of low pressure with multiple vorticies.

203900 1939N 09339W 9624 00363 0031 233 231 290002 003 011 008 00

I'm not seeing what you're seeing. Looks like one small but closed low-level circulation?

Member Since: July 6, 2010 Posts: 113 Comments: 32802
Wow, I just joined the ban train. Sorry folks, it was not blistering sarcasm. I was responding as a jest to an earlier post. Sheesh, I only post like twice a year. Oh well, I appologise to all.
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Quoting 765. Hurricanes305:


Really? I don't have access to detailed Recon assessment but that pressure might be contaminated.


Yea the lowest i see right now is 1004.6...
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Quoting 756. MiamiHurricanes09:
Pressure down to 1003.1mb now. Looks like 93L is actually a lot more disorganized than previously thought. Could be a large area of low pressure with multiple vorticies.

203900 1939N 09339W 9624 00363 0031 233 231 290002 003 011 008 00


Really? I don't have access to detailed Recon assessment but that pressure might be contaminated.
Member Since: Posts: Comments:
Quoting 761. CybrTeddy:


Which is strange, ASCAT showed a relatively tight low pressure area. Doesn't look like the NHC will upgrade it to 10L for now.
Kind of reminds me of Alex from 2010. Once it organized its core structure, it may really take off.
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Quoting 747. daddyjames:


Hey Mr. Mixon - first fires and now floods? What's next on "the apocalypse is now" list?

In all seriousness, you and your loved ones stay safe.


Thanks. It really has been a year of extremes around here. As I posted above, the latest tragedy is the cancellation of a significant beer-related event...
Member Since: March 26, 2006 Posts: 44 Comments: 1520

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
eastern Frederick County in north central Maryland...
Carroll County in north central Maryland...
northwestern Baltimore County in northern Maryland...

* until 515 PM EDT

* at 426 PM EDT... severe thunderstorms were detected along a line
extending from 8 miles northwest of Manchester to 15 miles
southwest of Westminster... and were moving east at 25 mph. This
line of storms is capable of producing damaging winds in excess of
70 mph.

* Locations impacted include...
Westminster...
Manchester...
Hampstead...

Gamber...
Eldersburg...
Oakland...
Reisterstown...
Owings Mills...
Randallstown...
Milford mill...

Precautionary/preparedness actions...

This is a dangerous line of storms. If you are in its path... prepare
immediately for damaging wind gusts and frequent cloud to ground
lightning. Move indoors to a sturdy building and stay away from
windows.
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Quoting 756. MiamiHurricanes09:
Pressure down to 1003.1mb now. Looks like 93L is actually a lot more disorganized than previously thought. Could be a large area of low pressure with multiple vorticies.



Which is strange, ASCAT showed a relatively tight low pressure area. Doesn't look like the NHC will upgrade it to 10L for now.
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760. HadesGodWyvern (Mod)
97W (future Man-Yi) is steadily improving and could go right over Fukushima at some time




already occurring as tropical cyclone Man-yi
Member Since: May 24, 2006 Posts: 52 Comments: 46906
From Steve Weagle on FB
Two funnel clouds reported near #Palm City and now a Funnel clouds possible near #Belle Glade and #Pahokee
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Quoting 744. LAbonbon:


More like 2 Allisons :O


That is Claudette totals! Alvin, TX had 43" of rain in 24 hours from Claudette. Setting the record for the highest rainfall total in a 24 hour period in U.S History. That record still stands today.
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Quoting 746. Ameister12:
Pasch is forecasting that Humberto will begin to restrengthen by 120h.

INIT 12/2100Z 23.1N 29.2W 75 KT 85 MPH
12H 13/0600Z 24.1N 30.3W 70 KT 80 MPH
24H 13/1800Z 25.2N 32.0W 65 KT 75 MPH
36H 14/0600Z 26.0N 34.2W 55 KT 65 MPH
48H 14/1800Z 26.8N 36.5W 45 KT 50 MPH
72H 15/1800Z 28.8N 40.8W 45 KT 50 MPH
96H 16/1800Z 30.5N 43.5W 45 KT 50 MPH
120H 17/1800Z 33.0N 45.0W 50 KT 60 MPH

$$
FORECASTER PASCH
Humberto will be forgot very soon.
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Pressure down to 1003.1mb now. Looks like 93L is actually a lot more disorganized than previously thought. Could be a large area of low pressure with multiple vorticies.

203900 1939N 09339W 9624 00363 0031 233 231 290002 003 011 008 00
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OK, how do you know when things are really bad?

This...



When the weather is bad enough to stop people from talking about and drinking beer, you know the weather is bad.
Member Since: March 26, 2006 Posts: 44 Comments: 1520
Quoting 727. txjac:


That's Allison rainfal amounts ...


The 40'' of rain is what some places get in a year in just 5 days. Lets hope it does not amount to so much.
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Quoting 654. NttyGrtty:
I figured that but I'm just trying to understand how any information outlet can be perceived so wrong on so many levels and still have a a majority audience. Kind out a human factors evaluation on my part...

For every person in America that watches Fox there are roughly 99 that do not.

Do the math.
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YESSSSSSSSS!!!! RAIN!!!!!!! AND POTENTIAL HAIL!!!

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97W (future Man-Yi) is steadily improving and could go right over Fukushima at some time:

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Quoting 749. Torito:


It might have a run at Cat 2 or something way down the road. :P

Seems very possible. A major hurricane isn't out of the question either.
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Quoting 746. Ameister12:
Pasch is forecasting that Humberto will begin to restrengthen by 120h.

INIT 12/2100Z 23.1N 29.2W 75 KT 85 MPH
12H 13/0600Z 24.1N 30.3W 70 KT 80 MPH
24H 13/1800Z 25.2N 32.0W 65 KT 75 MPH
36H 14/0600Z 26.0N 34.2W 55 KT 65 MPH
48H 14/1800Z 26.8N 36.5W 45 KT 50 MPH
72H 15/1800Z 28.8N 40.8W 45 KT 50 MPH
96H 16/1800Z 30.5N 43.5W 45 KT 50 MPH
120H 17/1800Z 33.0N 45.0W 50 KT 60 MPH

$$
FORECASTER PASCH


It might have a run at Cat 2 or something way down the road. :P
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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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