Red River rising: 18th consecutive year of flooding--why?

By: Dr. Jeff Masters , 3:08 PM GMT on March 19, 2010

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The Red River at Fargo, North Dakota continues to rise, with a peak expected Sunday at the 4th highest flood level observed in the past century. "Major" flood level is 30 feet, which the river surpassed on Wednesday, and the river is expected to crest near 38 feet on Sunday, just 2.8 feet below the record set last year. Flood stage is eighteen feet, and the Red River has now reached flood stage at Fargo for eighteen consecutive years, according to the U.S. Army Corps of Engineers. Prior to this remarkable stretch of flooding (which began in 1993), the river flooded in just 29 of 90 years. This year's flood is rated as somewhere between a 50-year and 100-year flood. Last year's record flood was a 100-year flood. The U.S. Army Corps of Engineers lists the 10-year flood level for the Red River at Fargo to be 10,300 cubic feet per second. A 10-year flood, historically, has a 10% chance of occurring in a given year. In the last twenty years, the Red River has had eight 10-year floods--one every 2.5 years, on average. This year is the fourth year out of the past five with a 10-year flood. Clearly, flooding has increased significantly along the Red River over the past twenty years.


Figure 1. Current and forecast flood stage for the Red River of the North at Fargo, ND. You can access images like these using our wundermap for Fargo with the "USGS River" layer turned on. Click on the icon for USGS station 05054000, then hit the "click for graph" link.

Reasons for flooding: landform factors
According the U.S. Geological Survey, the unique landform characteristics of the Red River Valley make it highly susceptible to flooding. These factors include:

1) A relatively shallow and meandering river channel--a shallow channel holds less water and the meandering can cause flow to slow down as the channel makes its turns, causing over-bank flooding.

2) A gentle slope (averaging 0.5 to 1.5 feet per mile) that inhibits channel flow and encourages overland flooding or water "ponding" (especially on even, saturated ground) in the basin.

3) The northerly direction of flow--flow in the Red River travels from south (upstream) to north (downstream). The direction of flow becomes a critical factor in the spring when the southern (upstream) part of the Red River has thawed and the northern (downstream) part of the channel is still frozen. As water moves north toward the still frozen river channel, ice jams and substantial backwater flow and flooding can occur.


Figure 2. Peak flow of the Red River at Fargo, North Dakota through time. The two largest flow rates occurred last year (2009), and in 1997. The projected crest for Sunday (red circle) would be fourth greatest flood since reliable records began in 1901. Image credit: U.S. Geological Survey.

Reasons for this year's flood: highly unfavorable weather conditions
The USGS also cites five weather factors that can act to enhance flooding along the Red River. All five of these factors occurred to a significant degree this year:

1) Above-normal amounts of precipitation in the fall of the year that produce high levels of soil moisture, particularly in flat surface areas, in the basin. North Dakota had its 22nd wettest fall in the 115-year record in 2009.

2) Freezing of saturated ground in late fall or early winter, before significant snowfall occurs, that produces a hard, deep frost that limits infiltration of runoff during snowmelt. Fargo had a November that was much warmer than average, followed by a sudden plunge to below-zero temperatures by the second week of December. This froze the saturated ground to a great depth.

3) Above-normal winter snowfall in the basin. North Dakota had a top 15% winter for precipitation, with the period December 2009 - February 2010 ranking 15th wettest in the past 115 years.

4) Above-normal precipitation during snowmelt. Precipitation for March 1 - 18 has been 1.41", compared to the average of 0.61".

5) Above-normal temperatures during snowmelt. High temperatures in Fargo have averaged 6°F warmer than normal for March 1 - 18.

Urbanization increases flooding
Urbanization has had a major impact on increasing flooding not only along the Red River, but in every river basin in the U.S. Many cities and developed areas are located in flood plains next to major rivers and their tributaries. Highways, streets, parking lots, sidewalks, and buildings now cover large areas of the ground that used to absorb excess rain water and slow the rate at which run-off from precipitation and melting snow reached rivers. By developing large portions of our flood plains, run-off now reaches rivers more quickly, generating higher floods.

Building levees and flood defenses increases flood peaks
Defending ourselves against floods has made floods worse. Every time a new levee is built, or an old floodwall raised in height to prevent overtopping, more and more water is forced into the river bed, which raises the height of the flood. Flood waters that used to be able to spread out over their natural flood plains are now forbidden from spilling out over newly developed land in flood plains. For example, proposed improvements to the flood defense system in Fargo could cause a 4 - 10 inch rise in floods immediately downstream from the city, according to the Army Corps of Engineers.

Precipitation is increasing
As the climate warms, evaporation of moisture from the oceans increases, resulting in more water vapor in the air. According to the 2007 IPCC report, water vapor in the global atmosphere has increased by about 5% over the 20th century, and 4% since 1970. Satellite measurements (Trenberth et al., 2005) have shown a 1.3% per decade increase in water vapor over the global oceans since 1988. Santer et al. (2007) used a climate model to study the relative contribution of natural and human-caused effects on increasing water vapor, and concluded that this increase was "primarily due to human-caused increases in greenhouse gases". This was also the conclusion of Willet et al. (2007). This increase in water vapor has very likely led to an increase in global precipitation. For instance, over the U.S., where we have very good precipitation records, annual average precipitation has increased 7% over the past century (Groisman et al., 2004). Precipitation over the Red River drainage basin increased by about 10 - 20% during the 20th Century (Figure 3.) The same study also found a 14% increase in heavy (top 5%) and 20% increase in very heavy (top 1%) precipitation events over the U.S. in the past century. These are the type of events most likely to cause flooding. Kunkel et al. (2003) also found an increase in heavy precipitation events over the U.S. in recent decades, but noted that heavy precipitation events were nearly as frequent at the end of the 19th century and beginning of the 20th century, though the data is not as reliable back then.


Figure 3. Change in precipitation over the U.S. between 1900 - 2000, from the U.S. Cooperative network. Precipitation in the Red River drainage area increased by 10 - 20% over the 20th century. Image credit: Contemporary Changes of the Hydrological Cycle over the Contiguous United States: Trends (Groisman et al., 2002).

The future of flooding
As the population continues to expand, development in flood plains and construction of new levees and flood protection systems will continue to push floods to higher heights. With global warming expected to continue and drive ever higher precipitation amounts--falling preferentially in heavy precipitation events--it is highly probable that flooding in the Red River Valley--and over most of the northern 2/3 of the U.S. where precipitation increases are likely--will see higher and more frequent floods. With these higher and more frequent floods comes the increased risk of multi-billion dollar disasters, when a record flood event overwhelms flood defenses and inundates huge areas of developed flood plains. Obviously, we need to make smart decisions to limit development in flood plains to reduce the cost and suffering of these future flooding disasters.

References
Kunkel, K. E., D. R. Easterling, K. Redmond, and K. Hubbard, 2003, "Temporal variations of extreme precipitation events in the United States: 1895.2000", Geophys. Res. Lett., 30(17), 1900, doi:10.1029/2003GL018052.

Groisman, P.Y., R.W. Knight, T.R. Karl, D.R. Easterling, B. Sun, and J.H. Lawrimore, 2004, "Contemporary Changes of the Hydrological Cycle over the Contiguous United States: Trends Derived from In Situ Observations," J. Hydrometeor., 5, 64.85.

Milly, P.C.D., R.T. Wetherald, K.A. Dunne, and T.L.Delworth, Increasing risk of great floods in a changing climate", Nature 415, 514-517 (31 January 2002) | doi:10.1038/415514a.

Santer, B.D., C. Mears, F. J. Wentz, K. E. Taylor, P. J. Gleckler, T. M. L. Wigley, T. P. Barnett, J. S. Boyle, W. Brüggemann, N. P. Gillett, S. A. Klein, G. A. Meehl, T. Nozawa, D. W. Pierce, P. A. Stott, W. M. Washington, and M. F. Wehner, 2007, "Identification of human-induced changes in atmospheric moisture content", PNAS 2007 104: 15248-15253.

Trenberth, K.E., J. Fasullo, and L. Smith, 2005: "Trends and variability in column-integrated atmospheric water vapor", Climate Dynamics 24, 741-758.

Willett, K.M., N.P. Gillett, P.D. Jones, and P.W. Thorne, 2007, "Attribution of observed surface humidity changes to human influence", Nature 449, 710-712 (11 October 2007) | doi:10.1038/nature06207.

Links
A good way to track the flooding event is to use our wundermap for the Red River with the USGS River layer turned on.

The Fargo Flood webpage of North Dakota State University, Fargo, has some excellent links.

I'll have a new post on Monday or Tuesday.

Jeff Masters

Red River Flood 2006 (mw25)
The water level of the Red River when I took this photo was 47.2 feet, 19.2 feet above flood stage and the 6th highest level in Grand Forks' history. The river is expected to crest at 47.4 feet on Wednesday morning. Luckily, no homes have been lost in the Grand Forks area as of yet due to the flooding.
Red River Flood 2006
Fargo Flood 2009 - Elm & 15th Ave. N. (tliebenow)
Picture says it all. Clay dike built to contain the Red River in North Fargo.
Fargo Flood 2009 - Elm & 15th Ave. N.

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Quoting Tropicsweatherpr:
Tropical Cyclone Formation Alert for Invest 98W.

WTPN21 PGTW 202300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
210 NM EITHER SIDE OF A LINE FROM 4.3N 146.7E TO 7.1N 138.7E WITHIN
THE NEXT 12 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF
NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME. WINDS IN THE AREA
ARE ESTIMATED TO BE 20 TO 25 KNOTS. METSAT IMAGERY AT 202030Z
INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 4.6N 145.6E. THE
SYSTEM IS MOVING WESTWARD AT 15 KNOTS.
2. REMARKS: THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 3.9N
148.5E, IS NOW LOCATED NEAR 4.6N 145.6E, APPROXIMATELY 530 NM EAST-
SOUTHEAST OF YAP. RECENT ANIMATED INFRARED SATELLITE IMAGERY SHOWS
DEEP CONVECTION HAS STARTED TO QUICKLY DEVELOP OVER AN ORGANIZING
LOW LEVEL CIRCULATION CENTER (LLCC). A 202014Z SSMI 37H MICROWAVE
PASS SHOWED A DEEP BAND OF CONVECTION ALONG THE NORTHERN HALF OF THE
LLCC WAS STARTING TO WRAP TOWARDS THE CENTER. UPPER LEVEL ANALYSIS
SHOWS THE LLCC IS UNDER A REGION OF FAVORABLE DIFFLUENCE ALONG THE
SOUTHWESTERN QUADRANT OF AN ANTICYCLONE. VERTICAL WIND SHEAR IS
LOW TO MODERATE (15 KNOTS) AND IS HELPING TO ENHANCE THE POLEWARD
OUTFLOW CHANNEL FOR THE LLCC. SEA SURFACE TEMPERATURE/OCEAN HEAT
CONTENT ARE FAVORABLE IN THE VICINITY OF THE LLCC AND WILL CONTINUE
TO ENHANCE THE CURRENT DEVELOPMENT OF DEEP CONVECTION. MAXIMUM
SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO 25 KNOTS. MINIMUM SEA
LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1005 MB. BASED ON THE DEVE-
LOPING DEEP CONVECTION AND FAVORABLE UPPER LEVEL SUPPORT, THE POTEN-
TIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN
THE NEXT 24 HOURS IS GOOD.


Was kind of expecting that to occur
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latest gfs. all slides will be there soon.
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Tropical Cyclone Formation Alert for Invest 98W.

WTPN21 PGTW 202300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
210 NM EITHER SIDE OF A LINE FROM 4.3N 146.7E TO 7.1N 138.7E WITHIN
THE NEXT 12 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF
NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME. WINDS IN THE AREA
ARE ESTIMATED TO BE 20 TO 25 KNOTS. METSAT IMAGERY AT 202030Z
INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 4.6N 145.6E. THE
SYSTEM IS MOVING WESTWARD AT 15 KNOTS.
2. REMARKS: THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 3.9N
148.5E, IS NOW LOCATED NEAR 4.6N 145.6E, APPROXIMATELY 530 NM EAST-
SOUTHEAST OF YAP. RECENT ANIMATED INFRARED SATELLITE IMAGERY SHOWS
DEEP CONVECTION HAS STARTED TO QUICKLY DEVELOP OVER AN ORGANIZING
LOW LEVEL CIRCULATION CENTER (LLCC). A 202014Z SSMI 37H MICROWAVE
PASS SHOWED A DEEP BAND OF CONVECTION ALONG THE NORTHERN HALF OF THE
LLCC WAS STARTING TO WRAP TOWARDS THE CENTER. UPPER LEVEL ANALYSIS
SHOWS THE LLCC IS UNDER A REGION OF FAVORABLE DIFFLUENCE ALONG THE
SOUTHWESTERN QUADRANT OF AN ANTICYCLONE. VERTICAL WIND SHEAR IS
LOW TO MODERATE (15 KNOTS) AND IS HELPING TO ENHANCE THE POLEWARD
OUTFLOW CHANNEL FOR THE LLCC. SEA SURFACE TEMPERATURE/OCEAN HEAT
CONTENT ARE FAVORABLE IN THE VICINITY OF THE LLCC AND WILL CONTINUE
TO ENHANCE THE CURRENT DEVELOPMENT OF DEEP CONVECTION. MAXIMUM
SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO 25 KNOTS. MINIMUM SEA
LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1005 MB. BASED ON THE DEVE-
LOPING DEEP CONVECTION AND FAVORABLE UPPER LEVEL SUPPORT, THE POTEN-
TIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN
THE NEXT 24 HOURS IS GOOD.

Member Since: April 29, 2009 Posts: 75 Comments: 13274
Quoting StormW:


1.) At the moment, I don't think there is a Kelvin wave, however the winds over that way are pretty much still out of the west, which is helping keep warm water pushed east. Usually see a Kelvin Wave when the SOI takes a strong dive negative, indicating a westerly wind burst:



2.) Once the SOI gets closer to neutral or goes positive

3.) A reactionary Nino, is one where the SST's react to what is happening with the state of the atmosphere, what we call a "top, down" effect. The state of the atmosphere brought this El Nino to life. A true oceanic El Nino is when the water gets warm at the Equatroial Pacific, then that heat causes the atmosphere to react.

4.) In my professional opinion...no.

5.) No.


Thank you Storm for the answers.
Member Since: April 29, 2009 Posts: 75 Comments: 13274
Quoting Midweststorm:
Here it is, first day of spring and we have 4 inches of snow in downtown Kansas City. Been quite some time since I have seen any accumulating snow here in March. And of course it is still snowing, they expect 5-8 inches before its all done.


!!!???

Upstate new york, we havent had snow for 2 weeks and it hasnt snowed in a month. It's been near 60 degrees and sunny all week.
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Is there seismic activity where ului approached?

Member Since: September 22, 2005 Posts: 11 Comments: 2032
Here it is, first day of spring and we have 4 inches of snow in downtown Kansas City. Been quite some time since I have seen any accumulating snow here in March. And of course it is still snowing, they expect 5-8 inches before its all done.
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703. xcool
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Quoting Stormchaser2007:
WPAC invest consolidating




Yea its pretty far south, so it should be interesting to watch
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WPAC invest consolidating


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699. HadesGodWyvern (Mod)
Tropical Cyclone Warning Center Brisbane
Tropical Cyclone Warning
Tropical Cyclone Ului, CAT 1
8:00 AM EST March 21 2010
=====================================

At 21:00 PM UTC, Tropical Cyclone Ului, Category 1 (992 hPa) located at 20.6S 147.3E or 120 kms southeast of Bowen and 60 kms west of Collinsville has 10 minute sustained winds of 45 knots with gusts of 65 knots. The cyclone is reported as moving west southwest at 15 knots.

Tropical Cyclone Ului is located west of Collinsville, and continuing to move further inland. The cyclone is weakening rapidly, and is expected to be downgraded below cyclone strength in the next hour or two.

DAMAGING winds are expected over adjacent inland areas between Ayr and Bowen for the next few hours.

HEAVY RAINFALL and flooding are likely to continue about coastal and adjacent inland areas between Bowen and St Lawrence.

DANGEROUS SURF conditions are expected to continue about exposed beaches south of the cyclone until later today. A separate Severe Weather Warning is current for these conditions.

Tropical Cyclone Watches
===========================
A Cyclone WARNING continues for coastal areas from Ayr to Bowen and adjacent inland areas.

The Cyclone WARNING from Bowen to Mackay has been cancelled.
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Homes damaged in Cyclone Ului: minister

QUEENSLAND Emergency Services Minister Neil Roberts says Cyclone Ului has caused damage to some homes in the Whitsundays but details remain sketchy.

About 60,000 homes are without power after Ului crossed the coast as a category three system with winds of 200km/h near Airlie Beach early this morning.

Mr Roberts says damage reports are starting to come in, but the picture is still hazy.

"The early reports we're getting in is minor to moderate damage in a number of homes, power outages across the region," he told the ABC.

"The SES had about 600 calls so far but we are expecting that to escalate significantly as daylight approaches."

He said the potential for flooding from heavy rains brought by the cyclone was now a primary concern.

Mr Roberts, Premier Anna Bligh and the acting chief officer of Emergency Management Queensland, Bruce Grady, will hold a phone hook-up with affected communities this morning.



The highest wind Obs from Mackay was 43kts with gusts of 57kts@1:58am

Proserpine had 49kts Gusts 79kts @2:30am
Member Since: September 30, 2007 Posts: 9 Comments: 15742
Beautiful day here in Lake Worth! Forecasted to be cloudy, windy and rainy tomorrow. Then another little cool down on Monday with highs in the mid 60's.

Local Text Forecast for
Lake Worth, FL (33461)

Mar 20 Tonight
Mainly clear skies. Low 63F. Winds ESE at 5 to 10 mph.
Mar 21 Tomorrow
Sunshine and clouds mixed. A stray shower or thunderstorm is possible. High around 80F. Winds SE at 20 to 30 mph.
Mar 21 Tomorrow night
Showers and a few thundershowers. Low 63F. Winds S at 10 to 20 mph. Chance of rain 60%.
Mar 22 Monday
Cloudy with showers and thunderstorms.. Highs in the mid 60s and lows in the mid 50s.
Mar 23 Tuesday
Sunny. Highs in the low 70s and lows in the mid 50s.
Mar 24 Wednesday
Partly cloudy. Highs in the mid 70s and lows in the upper 50s.
Mar 25 Thursday
Mix of sun and clouds. Highs in the mid 70s and lows in the low 60s.
Mar 26 Friday
Times of sun and clouds. Highs in the mid 70s and lows in the low 60s.
Mar 27 Saturday
Isolated thunderstorms. Highs in the upper 70s and lows in the low 60s.
Mar 28 Sunday
Mix of sun and clouds. Highs in the upper 70s and lows in the low 60s.
Mar 29 Monday
Considerable cloudiness. Highs in the mid 70s and lows in the low 60s.
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Quoting Skyepony:
I never could find a cam in Ului's eye path.

Member Since: September 30, 2007 Posts: 9 Comments: 15742
Quoting caribbeantracker01:
A TROPICAL WAVE THE FIRST ONE I BELIEVE OF 2010 LOOK AT THE SURFACE MAPS


The CMC intensifies it to cat5 and direct hit New Orleans, then moving ESE to affect Miami, then turning north up the coast and reintensifying to a cat 6 and hit just west of Manhattan.



...gotta love the CMC doom-casts though. I miss them. If I remember correctly the model does that because it's designed to handle systems at the latitude of canada, which act differently than systems in the tropics.

While I'm on the topic, what's the best site for looking at a bunch of different model animations? Like GFS, UKMET, and a few others... precipitation map, or whatever.
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Quoting Drakoen:


it's coming in:



Thanks Drak!! It is very windy right now, wind chills in the mid 20's, gusts to near 35-40MPH! Great first day of Spring 2010!
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting Bordonaro:
While we're all getting ready for the 2010 Atlantic Hurricane Season, which will be alot more lively than 2009, it's a crisp 37F here in Arlington, TX, NW winds 20 MPH G to 35 MPH, overcast with an occasional burst of snow flurries!


it's coming in:

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Quoting Levi32:


Yes.


Alright thanks.

Last year it was closer to Mid-April
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While we're all getting ready for the 2010 Atlantic Hurricane Season, which will be alot more lively than 2009, it's a crisp 37F here in Arlington, TX, NW winds 20 MPH G to 35 MPH, overcast with an occasional burst of snow flurries!
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting Levi32:


Yes I think we were talking about it the other day. Cold anomalies off the west coast argue for lower heights and a suppressed jet, and hence more troughing over the western US. This teleconnects to more ridging over the SE US. This pattern is characteristic of a cold PDO.

I have to wonder if an East Coast threat seems likely. With this setup, once the El Nino subsides I wouldnt be surprised if a heat dome sets up over the gulf coast states just west of an east coast trough. No way to tell now, but something to watch for.
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685. xcool
Levi32 thank .i'm back now .my son was cry .
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Quoting Stormchaser2007:
Dr.Grey and TSR come out with their forecasts in early April correct?


Yes.
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Quoting SouthALWX:
I was wondering before and never received an answer ... Given the colder anomalies in the NE Pac, wouldnt that induce a general troughing over the US and encourage more fish storms? Or would it imply a west coast trough? Or none at all? I really dont know but I think it may be important =P


Yes I think we were talking about it the other day. Cold anomalies off the west coast argue for lower heights and a suppressed jet, and hence more troughing over the western US. This teleconnects to more ridging over the SE US. This pattern is characteristic of a cold PDO.
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Dr.Grey and TSR come out with their forecasts in early April correct?
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??? Had to some see what the shouting is all about.
Oh.

Whatever. Carry on.
*weekend, un-pause*
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Quoting Hurricanes101:


Everything is there but the "table above" which it looks like actually shows us what their prediction is for the season lol


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I was wondering before and never received an answer ... Given the colder anomalies in the NE Pac, wouldnt that induce a general troughing over the US and encourage more fish storms? Or would it imply a west coast trough? Or none at all? I really dont know but I think it may be important =P
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A TROPICAL WAVE THE FIRST ONE I BELIEVE OF 2010 LOOK AT THE SURFACE MAPS
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Quoting xcool:
ImpactWeather’s 2010 Atlantic Hurricane Season Outlook


Contributing Factors In Our Forecast

• Water Temperatures Over the Main Development Region (MDR)
• Wind Shear

Water Temperatures Warmer Than Normal
As with any hurricane season forecast, one of the primary tools we use to make our prognosis is the study of water temperature anomalies in the MDR. Compared to last year at this time, water temperature anomalies are currently averaging from 2.0 to 3.0C (3.6 to 5.4F) higher, meaning there is considerably more available heat content for tropical cyclones to develop. We expect these warmer than normal sea surface temperatures to persist through the hurricane season.

Wind Shear Lower Than Normal
One of the main indicators utilize to determine the intensity of wind shear in any given tropical season is whether there will be an El Niño. The presence of an El Niño will produce higher westerly wind shear, resulting in a net reduction of named tropical cyclones. There is currently a moderate El Niño in place across the Pacific Ocean, but we expect it to quickly weaken this spring and likely dissipate by the summer. So El Niño should not be much of a factor. Over the Atlantic, we expect the Bermuda High to average a little weaker than normal, which should result in slightly less easterly low-level wind shear over the MDR. This may play a role in keeping the Tropical Atlantic a bit more active.

Our Forecast
Detailed analysis of expected water temperature profiles across both the Atlantic and Pacific Oceans combined with wind shear forecasts for this tropical season have allowed us to identify several analog seasons. (An analog season is a past hurricane season with atmospheric pressure patterns and sea surface temperatures closely resembling the current pattern.) The development patterns and general movement of storms in an analog season can provide significant insight about what we might expect over the coming season. Depending upon how closely an analog season approximates the current conditions, we can establish weighting factors for each of these analogs in deriving our preliminary forecast. We have identified 5 potential analog seasons that will be used in our forecast. Our primary analog season (1958) has a weighting factor of 30% of the total forecast, while our lowest analog seasons (1995 and 2003) each only have a 12.5% weighting factor of the total. The result is the number of storms shown in the table above.

An “average” hurricane season consists of 11 named storms, 6 hurricanes and 2 major hurricanes.

The Hurricane Severity Index
After the devastating 2005 hurricane season, ImpactWeather developed a new hurricane scale that takes into account both the intensity and the wind field size of a tropical storm or hurricane. We call this scale the Hurricane Severity Index, or HSI for short. The HSI is a 50-point scale, allowing for up to 25 points for a tropical cyclones maximum sustained wind and up to 25 points for the size of its wind field. Based on the generally favorable environment for development in 2010, we have made some estimates of the peak HSI for this season’s tropical cyclones


Chris Hebert


Everything is there but the "table above" which it looks like actually shows us what their prediction is for the season lol
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Invest 98W




Member Since: July 3, 2005 Posts: 414 Comments: 125503
Ului now inland with is core still intact,..as dawn approaches..

Member Since: July 3, 2005 Posts: 414 Comments: 125503
674. xcool
ImpactWeather’s 2010 Atlantic Hurricane Season Outlook


Contributing Factors In Our Forecast

• Water Temperatures Over the Main Development Region (MDR)
• Wind Shear

Water Temperatures Warmer Than Normal
As with any hurricane season forecast, one of the primary tools we use to make our prognosis is the study of water temperature anomalies in the MDR. Compared to last year at this time, water temperature anomalies are currently averaging from 2.0 to 3.0C (3.6 to 5.4F) higher, meaning there is considerably more available heat content for tropical cyclones to develop. We expect these warmer than normal sea surface temperatures to persist through the hurricane season.

Wind Shear Lower Than Normal
One of the main indicators utilize to determine the intensity of wind shear in any given tropical season is whether there will be an El Niño. The presence of an El Niño will produce higher westerly wind shear, resulting in a net reduction of named tropical cyclones. There is currently a moderate El Niño in place across the Pacific Ocean, but we expect it to quickly weaken this spring and likely dissipate by the summer. So El Niño should not be much of a factor. Over the Atlantic, we expect the Bermuda High to average a little weaker than normal, which should result in slightly less easterly low-level wind shear over the MDR. This may play a role in keeping the Tropical Atlantic a bit more active.

Our Forecast
Detailed analysis of expected water temperature profiles across both the Atlantic and Pacific Oceans combined with wind shear forecasts for this tropical season have allowed us to identify several analog seasons. (An analog season is a past hurricane season with atmospheric pressure patterns and sea surface temperatures closely resembling the current pattern.) The development patterns and general movement of storms in an analog season can provide significant insight about what we might expect over the coming season. Depending upon how closely an analog season approximates the current conditions, we can establish weighting factors for each of these analogs in deriving our preliminary forecast. We have identified 5 potential analog seasons that will be used in our forecast. Our primary analog season (1958) has a weighting factor of 30% of the total forecast, while our lowest analog seasons (1995 and 2003) each only have a 12.5% weighting factor of the total. The result is the number of storms shown in the table above.

An “average” hurricane season consists of 11 named storms, 6 hurricanes and 2 major hurricanes.

The Hurricane Severity Index
After the devastating 2005 hurricane season, ImpactWeather developed a new hurricane scale that takes into account both the intensity and the wind field size of a tropical storm or hurricane. We call this scale the Hurricane Severity Index, or HSI for short. The HSI is a 50-point scale, allowing for up to 25 points for a tropical cyclones maximum sustained wind and up to 25 points for the size of its wind field. Based on the generally favorable environment for development in 2010, we have made some estimates of the peak HSI for this season’s tropical cyclones


Chris Hebert
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Swath pushing to the south and east:




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I have questions about what is going on with ENSO that the experts here can answer.

1-Is there another kevin wave causing the waters to keep warm?

2-Is it known when those kevin waves stop?

3-What is a reactionary El Nino?

4-Are the ENSO models too fast fading El Nino?

5-Is it possible that this El Nino extends to a two year event?
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671. xcool
2010 hurricane season trouble "No "questions
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Unfortunately the Loop Current and Gulf Stream are showing up quite well in the midst of cold SSTs, meaning that the waters of the gulf and off the SE US coast will have no problem warming up during the spring and early summer.

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Quoting Stormchaser2007:

2010:


2005:


Wow! I like this discussion. It's getting me all excited for this season. I missed tracking storms. Could shape up to be a great season for trackers too. Cooler than normal temperatures all near the US coast, and warmer than normal where all the fish live.

Am just a bit nervous about that May-June western carribean storm we seem to have every year from a dying front. If it's sitting over a hot tub even with shear it could be a bad one!
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If we get something like this that the European is showing for the summer, it may not be pretty.

The areas cooler water in the eastern equatorial Pacific due to developing La Nina and north of 25N over the eastern Atlantic promote net sinking air, which forces air to move towards the area of net upward motion over the entire SW Atlantic associated with warmer-than-normal SSTs. This causes more surface convergence in this area which accelerates upward motion, and causes more clouds, precipitation, and ultimately, tropical cyclones.



You can see this pattern reflected by the sea-level pressures:

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667. xcool
What About? Bermuda-Azores high
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I don't know if anybody else knew this, but Ului struck Queensland the same day Tropical Cyclone Larry did so four years ago.


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Anomalously higher OLR certainly helps with warming in the MDR. Compare that with the negative OLR in the GOM hence the cooler temperatures in that region:

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The cold water to the north of the MDR is bad news too, as it helps focus surface convergence and upward air motion over the MDR, where the warmer waters are. This is actually worse than if the entire Atlantic Ocean were warmer than normal. That belt of cold water to the north is concerning.
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The Caribbean seems to really be warming up fast during the past month. We seem to be ahead of most seasons in terms of SST's as of now. If the SST's continue to warm at this rate and conditions permit, I wouldn't be surprised if we saw an early season storm or two develop in May.

Arthur (2008):
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661. xcool
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.