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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Fire & rain-New Jersey has a major fire along the boardwalk multiple structures involved and the Control Tower at a Baltimore airport has been shut down by the FAA due to a lightning strike.
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LLC is oval shaped, it appears?

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Quoting 688. Ameister12:

He has been very busy with college recently.


Had one last night.
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Quoting 695. prcane4you:
He likes NOLA.

He is NOT allowed in NOLA
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Quoting 682. hurricanehanna:


Keep Cantore away from the GOM ! LOL well, you could actually park him in Central TX if you want ;)
He likes NOLA.
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19.517N 92.983W 987.7 mb
(~ 29.17 inHg) 145 meters
(~ 476 feet) 1004.2 mb
(~ 29.65 inHg) - From 227° at 18 knots
(From the SW at ~ 20.7 mph) 23.7°C
(~ 74.7°F) 22.5°C
(~ 72.5°F) 19 knots
(~ 21.8 mph) 22 knots
(~ 25.3 mph)
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This one could catch us by surprise. It has a very well defined surface circulation. And being so weak, this could pass through the Caribbean, and then get picked up by a trough and go north towards major land areas.

2. THE SHOWER ACTIVITY ASSOCIATED WITH A BROAD AREA OF LOW PRESSURE
CENTERED ABOUT 450 MILES EAST OF THE LEEWARD ISLANDS REMAINS
LIMITED. ALTHOUGH SURFACE PRESSURES ARE STILL FALLING IN THE
AREA...ENVIRONMENTAL CONDITIONS ARE NOT FAVORABLE FOR DEVELOPMENT.
THIS DISTURBANCE HAS A LOW CHANCE...10 PERCENT...OF BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS. ALTHOUGH UPPER-LEVEL
WINDS COULD BECOME A LITTLE MORE FAVORABLE IN SEVERAL DAYS...THIS
SYSTEM STILL HAS A LOW CHANCE...20 PERCENT...OF BECOMING A TROPICAL
CYCLONE DURING THE NEXT 5 DAYS AS IT MOVES TOWARD THE
WEST-NORTHWEST.
Member Since: May 12, 2012 Posts: 11 Comments: 2841
What is an 'outflow channel,' and in what way does it enhance storm intensifcation?
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10L is deja vu ALL OVER AGAIN.

Member Since: October 6, 2007 Posts: 0 Comments: 6453
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.


I'd like to get a few more center fixes from the recon but that's my thinking as well.
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Looks like it's moving very slowly
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Quoting 685. duajones78413:
Where is Levi? havent seen a tidbit from him recently

College has been keeping him busy recently. However, he did do a Tidbit yesterday.
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Quoting 684. SFLWeatherman:
What is going on with EX-98L?? look at this EX-98L is at 55W and this is at 15N 57W Pressure is at 1004MB and falling

It should be reactivated soon and developed further may become our next named system
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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.
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Where is Levi? havent seen a tidbit from him recently
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What is going on with EX-98L?? look at this EX-98L is at 55W and this is at 15N 57W Pressure is at 1004MB and falling
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Not perfectly defined...but still sufficiently organized to be a tropical depression.

In my eyes at least.

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Quoting 675. prcane4you:
What an issue.Let me call Cantore.


Keep Cantore away from the GOM ! LOL well, you could actually park him in Central TX if you want ;)
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1004.9MB and dropping.

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Quoting 625. prcane4you:
35 mhp is a TS.

35kts, which is about 39mph, is the threshold for a TS.
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Theres the west winds!

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Quoting 672. hurricanes2018:
To go to Fishland.
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re: 617. GetReal 2:52 PM CDT on September 12, 2013
Quoting GetReal:



Looks pretty dead on there Doc... The swirl is slightly exposed on the Sw side of the convection.


GR, lol, my eyes ain't what dey used to be, but it seems close...

Dr Jeff is certainly right about potentially deadly flooding from this system. Wunderground's hurricane archives don't include them, but keep in mind - the deadliest storm of the 1999 season was unnamed Tropical Depression Eleven, caused over 400 deaths in Mexico...

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Quoting 668. Tazmanian:
I like too say am sorry if I de rail the blog too march early this AM I was not a wake yet fully now I am

apology accepted.
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Quoting 666. DavidHOUTX:


Lol.. 39mph is Tropical Storm status
What an issue.Let me call Cantore.
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Gonzo be flying in circles tomorrow......


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Quoting 668. Tazmanian:
I like too say am sorry if I de rail the blog too march early this AM I was not a wake yet fully now I am


It's ok Taz...we all have our days :)
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Slight kick-up of clouds off Central America is in an area of lowering shear -- barely seen here as it starts up off Nicaragua coastline. Still basically nothing. (not a good image of latest pics)

Meanwhile, shear seems to be increasing along TX coast, as per very last of loop.



  
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Some have explained that an inch or two of rain in Colorado is a big deal because our drainages are "flashy". This is true. Our soils are thin and our topography is steep, which means watersheds shed their water in a hurry, compared to other areas.

So think about this. An inch or two of rain is a big deal... and this is what we've gotten SO FAR...



...additional rain predictions I've heard range from 3-6" before this system is done with us sometime this weekend.
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I like too say am sorry if I de rail the blog too march early this AM I was not a wake yet fully now I am
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and we have the Westerlies....

Just in time for the NHC to declare it for the 5
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Quoting 652. prcane4you:
Ok.35+1 = TS.


Lol.. 39mph is Tropical Storm status
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665. VR46L


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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...
Agree.
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Latest models show slightly more NW track for 93L it seems. If that Low over CC, TX continues W, maybe it'll bring up rain on the back-side..
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Quoting 653. MiamiHurricanes09:
Looks like we have 10L...with a 1004mb pressure...winds near 30kts.

195430 1949N 09250W 9879 00153 0054 +227 //// 305006 009 /// /// 05
195500 1948N 09251W 9877 00152 0051 +231 +228 238009 010 /// /// 05
195530 1947N 09252W 9873 00155 0049 +230 +226 230010 012 /// /// 03
195600 1945N 09252W 9879 00149 0049 +226 //// 237015 016 /// /// 05
195630 1944N 09253W 9876 00148 0048 +226 //// 237014 017 /// /// 09
195700 1943N 09254W 9875 00149 0048 +222 +222 244019 020 /// /// 03
195730 1942N 09254W 9877 00146 0047 +219 //// 246016 019 /// /// 05
195800 1940N 09255W 9882 00143 0047 +223 //// 243015 017 /// /// 05
195830 1939N 09256W 9881 00144 0048 +217 //// 238015 016 /// /// 05
195900 1938N 09256W 9880 00145 0047 +224 +221 236016 017 023 011 00



whats see what else they find
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Quoting 635. EricSpittle:
Where are you located?

SE PA. This is the first time that I am under a warning and will actually get a storm
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here your W winds

From 238° at 9 knots
(From the WSW at ~ 10.3 mph) 23.1°C*
(~ 73.6°F*) 22.8°C*
(~ 73.0°F*) 10 knots
(~ 11.5 mph) - - - -
19:55:30Z 19.783N 92.867W 987.3 mb
(~ 29.15 inHg) 155 meters
(~ 509 feet) 1004.9 mb
(~ 29.67 inHg) - From 230° at 10 knots
(From the SW at ~ 11.5 mph) 23.0°C
(~ 73.4°F) 22.6°C
(~ 72.7°F) 12 knots
(~ 13.8 mph) - - - -
19:56:00Z 19.750N 92.867W 987.9 mb
(~ 29.17 inHg) 149 meters
(~ 489 feet) 1004.9 mb
(~ 29.67 inHg) - From 237° at 15 knots
(From the WSW at ~ 17.2 mph) 22.6°C*
(~ 72.7°F*) -* 16 knots
(~ 18.4 mph) - - - -
19:56:30Z 19.733N 92.883W 987.6 mb
(~ 29.16 inHg) 148 meters
(~ 486 feet) 1004.8 mb
(~ 29.67 inHg) - From 237°* at 14 knots*
(From the WSW* at ~ 16.1 mph*) 22.6°C*
(~ 72.7°F*) -* 17 knots*
(~ 19.5 mph*) - - - -
19:57:00Z 19.717N 92.900W 987.5 mb
(~ 29.16 inHg) 149 meters
(~ 489 feet) 1004.8 mb
(~ 29.67 inHg) - From 244° at 19 knots
(From the WSW at ~ 21.8 mph) 22.2°C
(~ 72.0°F) 22.2°C
(~ 72.0°F) 20 knots
(~ 23.0 mph) - - - -
19:57:30Z 19.700N 92.900W 987.7 mb
(~ 29.17 inHg) 146 meters
(~ 479 feet) 1004.7 mb
(~ 29.67 inHg) - From 246° at 16 knots
(From the WSW at ~ 18.4 mph) 21.9°C*
(~ 71.4°F*) -* 19 knots
(~ 21.8 mph) - - - -
19:58:00Z 19.667N 92.917W 988.2 mb
(~ 29.18 inHg) 143 meters
(~ 469 feet) 1004.7 mb
(~ 29.67 inHg) - From 243° at 15 knots
(From the WSW at ~ 17.2 mph) 22.3°C*
(~ 72.1°F*) -* 17 knots
(~ 19.5 mph) - - - -
19:58:30Z 19.650N 92.933W 988.1 mb
(~ 29.18 inHg) 144 meters
(~ 472 feet) 1004.8 mb
(~ 29.67 inHg) - From 238° at 15 knots
(From the WSW at ~ 17.2 mph) 21.7°C*
(~ 71.1°F*) -* 16 knots
(~ 18.4 mph) - - - -
19:59:00Z 19.633N 92.933W 988.0 mb
(~ 29.18 inHg) 145 meters
(~ 476 feet) 1004.7 mb
(~ 29.67 inHg) - From 236° at 16 knots
(From between the SW and WSW at ~ 18.4 mph)
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NOAAs RECON is in the air flying WNW
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Sharp windshift, so closed LLC confirmed. SFMR having problems though.
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Product: Air Force High Density (HDOB) Message (URNT15 KNHC)
Transmitted: 12th day of the month at 19:59Z
Date: September 12, 2013
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 302)
Mission Purpose: Investigate fifth suspect area (flight in the North Atlantic basin)

Mission Number: 1
Observation Number: 20

19:59:00Z 19.633N 92.933W 988.0 mb
(~ 29.18 inHg) 145 meters
(~ 476 feet) 1004.7 mb
(~ 29.67 inHg) - From 236° at 16 knots
(From between the SW and WSW at ~ 18.4 mph) 22.4°C
(~ 72.3°F) 22.1°C
(~ 71.8°F) 17 knots
(~ 19.5 mph) 23 knots
(~ 26.4 mph) 11 mm/hr
(~ 0.43 in/hr) 21.6 knots (~ 24.9 mph)
135.3%
Time Coordinates Aircraft
Static Air Pressure Aircraft
Geopotential Height Extrapolated
Surface Pressure D-value Flight Level Wind (30 sec. Avg.) Air Temp. Dew Point Peak (10 sec. Avg.)
Flight Level Wind SFMR
Peak (10s Avg.) Sfc. Wind SFMR
Rain Rate Estimated Surface Wind (30 sec. Avg.)
Using Estimated Reduction Factor Peak Wind at Flight Level to
Est. Surface Reduction Factor

HDOB Observations

Independent Calculations from Tropical Atlantic

At 19:49:30Z (first observation), the observation was 144 miles (232 km) to the N (5°) from Villahermosa, Tabasco, México.

At 19:59:00Z (last observation), the observation was 115 miles (184 km) to the N (0°) from Villahermosa, Tabasco, México.
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WSW winds now
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Quoting 636. prcane4you:
He meant may be he don't like Fox
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...
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Looks like we have 10L...with a 1004mb pressure...winds near 30kts.

195430 1949N 09250W 9879 00153 0054 +227 //// 305006 009 /// /// 05
195500 1948N 09251W 9877 00152 0051 +231 +228 238009 010 /// /// 05
195530 1947N 09252W 9873 00155 0049 +230 +226 230010 012 /// /// 03
195600 1945N 09252W 9879 00149 0049 +226 //// 237015 016 /// /// 05
195630 1944N 09253W 9876 00148 0048 +226 //// 237014 017 /// /// 09
195700 1943N 09254W 9875 00149 0048 +222 +222 244019 020 /// /// 03
195730 1942N 09254W 9877 00146 0047 +219 //// 246016 019 /// /// 05
195800 1940N 09255W 9882 00143 0047 +223 //// 243015 017 /// /// 05
195830 1939N 09256W 9881 00144 0048 +217 //// 238015 016 /// /// 05
195900 1938N 09256W 9880 00145 0047 +224 +221 236016 017 023 011 00
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Quoting 638. Tazmanian:



no

40mph is a TS


25mph to 35mph is a TD
Ok.35+1 = TS.
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650. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Advisory #15
Gale Warning
TROPICAL STORM MAN-YI (T1318)
3:00 AM JST September 13 2013
======================================

Ogasawara Waters

At 18:00 PM UTC, Tropical Storm Man-yi (1000 hPa) located at 21.0N 145.7E has 10 minute sustained winds of 35 knots with gusts of 50 knots. The cyclone is reported as moving west northwest at 7 knots.

Gale Force Winds
================
150 NM from the center

Dvorak intensity: T2.5

Forecast and Intensity
=======================
24 HRS: 23.3N 141.7E- 40 knots (CAT 1/Tropical Storm) Ogasawara Waters
48 HRS: 27.3N 137.9E- 50 knots (CAT 2/Severe Tropical Storm) Sea South Of Japan
72 HRS: 33.5N 140.0E- 50 knots (CAT 2/Severe Tropical Storm) Izu Islands Waters
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43 knots
(~ 49.4 mph)

Probably contaminated, but the baseline for rain contamination is 0.75in/hr where this was picked up in 0.51in/hr. Flight level winds don't reflect that strong of a system yet.

Not quite at where one would find the LLC per ASCAT yet.
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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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