RETURN OF LA NI�A

Blue area at center of Pacific Ocean shows cool sea surface temperatures along the equator during the 2007 La Ni�a. Credit: NASA/Goddard's Scientific Visualization Studio.

The powerful Pacific Ocean climate pattern known as La Ni�a returned in August, after briefly dipping into neutral territory last May. 

Yesterday's La Ni�a advisory from the Climate Prediction Center forecasts that the newborn La Ni�a�currently weak�will strengthen later this autumn and winter. 

Historic winter storm of 1-2 February 2011 moving across eastern US. Credit: NASA Earth Observatory.

  

A return to La Ni�a raises the possibility of more of the wild weather of last winter and spring�extreme blizzards, extreme tornadoes, extreme cold, extreme heat, extreme drought, extreme rainfall�around the globe.

Panoramic view from the International Space Station of east-central Texas on 6 September 2011, with numerous wildfire smoke plumes. Credit: NASA Earth Observatory.

  

Jeff Masters at his Wunderblog reminds us of some specifics:

Drought conditions are common over the southern tier of states during a La Ni�a event, since the cooling of the equatorial Pacific waters usually pushes the jet stream such that rain-bearing low pressure systems pass through the Midwest and avoid the South. It is likely that the drought gripping Texas, Oklahoma, and New Mexico will continue well into 2012, due to the emergence of La Ni�a. La Ni�a events also typically cause wetter than normal winters in the Pacific Northwest and Ohio Valley, colder winters in the Pacific Northwest and northern Plains, and warmer temperatures in the southern states. 

Hurricane Irene at Category 3 strength on 24 August 2011. Credit: NASA Earth Observatory.

   
La Nina is also one of the variables contributing to this year's extremely active hurricane season, with 14 named storms formed before the halfway mark. An average year sees 10 to 11 named storms in the entirety of the season. 

Elsewhere in the world, the last La Ni�a contributed to:

• Floods in Australia (one of that nation's worst natural disasters)
• Floods in Sri Lanka
• Floods in Brazil

Via.

  

It's also good to remember that a rejuvenated La Ni�a provides real bennies to some locales. 

Invigorated Pacific trade winds drive upwelling along the coast of South America, sending ocean productivity into overdrive and providing excellent conditions for plankton, fish, seabirds, and marine mammals�many of which will experience population booms.

El Ni�o conditions on top globe, La Ni�a conditions on bottom. Credit: NOAA.

  
Technically, La Ni�a is one third of the ENSO triad known as the El Ni�o/La Ni�a-Southern Oscillation. 

The El Ni�o/La Ni�a phases are characterized by variations in the sea surface temperatures of the tropical eastern Pacific:

• El Ni�o with warmer waters
• La Ni�a with cooler waters
• Neutral with neutral waters

The power of this oscillation is staggering�rearranging trade winds, rearranging ocean depths, rearranging ocean temperatures, and rearranging ocean productivity. 

The three diagrams below describe how that works.

Neutral conditions. Credit: NOAA.

 
Neutral conditions (above): Sea surface temperatures are higher in the Western Pacific than off South America. Trade winds blowing east to west along the equator allow the upwelling of cold nutrient-rich water from deep waters off the coast of South America. Trade winds push the ocean west, piling water up in the Western Pacific, with average sea-level heights running about 1.5 feet/0.5 meters higher off Indonesia than off Peru. A deep 450 feet/150 meter warm layer, known as a thermocline, forms in the west, while the thermocline in the east rises to 90 feet/30 meters. The shallow eastern thermocline allows the winds to pull up cooler nutrient-rich from below. 

La Ni�a conditions. Credit: NOAA.

 
La Ni�a conditions (above): Trade winds blowing west across the tropical Pacific are stronger than normal, leading to an even shallower thermocline in the east off South America, along with increased upwelling and lower than normal sea surface temperatures. Prevailing rain patterns shift farther west than normal. Winds pile up warm surface water in the Western Pacific.

 El Ni�o conditions. Credit: NOAA.

  

El Ni�o conditions (above): Air pressure at Darwin, Australia (Western South Pacific), is higher than at Tahiti (Central South Pacific). Trade winds decrease in strength and may reverse direction causing the normal flow of water away from South America to diminish and causing ocean water to pile up off South America, pushing the thermocline deeper, as upwelling dwindles. The flip in the thermocline and the decreased westward flow of water allow sea surface temperatures to rise higher than normal in the Eastern Tropical Pacific. The net result is a shift of the prevailing rain pattern, with the Central Pacific getting wetter as the Western Pacific gets drier.
    

Comparison of the 6 strongest La Ni�a events since 1950. Credit: Klaus Wolter, NOAA.

  
It's uncommon for one La Ni�a to follow on the heels of a prior La Ni�a�though it's less uncommon when the onset of the first La Ni�a is fast and really cold... which is how it went down last winter.   

Klaus Wolter, research scientist at the Climate Diagnostics Center at the University of Colorado, recreated conditions back to 1870 and found 10 cases in which La Ni�a lasted at least two consecutive years. He also found signs of persistent drought in the US Southwest in 8 of 10 of the double-dip La Ni�as.

Credit: Rmrfstar at Wikimedia Commons.

FIVE GOOD THINGS ABOUT A HURRICANE

Hurricane Felix over the coast of eastern Honduras. Credit: NASA via Universe Today.

  
1. Tropical cyclones are important rainmakers, providing 25 percent or more of available rainfall to places like Japan, India, and Southeast Asia�not to mention Texas, which desperately needs a dousing ASAP.
  

In the course of a year, low latitudes gain more heat and high latitudes loose more heat. Tropical cyclones help transport heat from the equator towards the poles. Credit: NASA.

  
2. Tropical cyclones help maintain the global heat balance by moving warm tropical air away from the equator and towards the poles. Without them, the tropics would get a lot hotter and the poles a lot colder... A typical tropical cyclone releases heat energy of about 50 to 200 exajoules a day. That's equivalent to 70 times our worldwide energy consumption.

Long Island, New York, with multiple barrier islands. Credit: NASA.

    
3. Paradoxically, fragile barrier islands need hurricanes for their survival�especially now, when sea levels are rising. Although hurricanes erode beaches on the ocean side of barrier islands, they build up the back sides of the same islands by depositing new sediments via winds and waves. This dynamical process keeps barrier islands alive.

Global thermohaline circulation, aka the ocean conveyor belt. Credit: Avsa via Wikimedia Commons.

    
4. Tropical cyclones stir up the ocean and drive the process of upwelling, thus playing a part in the thermohaline circulation�another important transport mechanism distributing heat between the equator and the poles and keeping the earth's temperature in better balance.

Mangroves, fish nurseries, can benefit from a hurricane's stirring of the waters. Credit: MIT-WHOI.

       
5. By stirring the ocean, tropical cyclones also cycle nutrients from the seafloor to the surface, boosting ocean productivity and setting the stage for blooms of marine life.

HURRICANE SKIES

Image links:

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15

STORM SURGE

Water vapor, showing massive footprint of Hurricane Irene at 1945 UTC on 25 Aug 2011. Credit: NOAA.

  
No matter where Hurricane Irene makes landfall it will likely impact a huge area of the East Coast. That's because the storm is so huge�and it's still growing�and because it's so slow moving.

These two factors amplify storm surge by inundating a lot of territory for a very long time.

Crescent moon. Credit: NASA.

  
Worse, Irene may well end up walloping the densely populated Northeast during the highest tides of the month�on Sunday's new moon.

If all the variables line up just wrong, this could lead to a catastrophic storm tide.

Storm surge versus storm tide. Credit: NOAA.

   
Meteorologist Jeff Masters, writing at his Wunderblog, warns:

I am most concerned about the storm surge danger to North Carolina, Virginia, Maryland, Delaware, New Jersey, New York, and the rest of the New England coast. Irene is capable of inundating portions of the coast under 10-15 feet of water, to the highest storm surge depths ever recorded.

Historical SLOSH (Sea, Lake, and Overland Surge from Hurricanes) animation from the 1938 New England hurricane. Credit: NOAA.

   
The 1938 New England hurricane (back in the days before naming), the only Cat 3 storm to hit the Northeast since the 1800s, drove a 15-foot storm surge onto Long Island.  

Above, you can see the extent of that surge from New York to Cape Cod. Here's an animated simulation of that.

Hand-drawn weather map of the 1938 Hurricane. Credit: NOAA.

 
Masters estimates a 20 percent chance that Irene will deliver a storm surge higher than 8 feet to New York City. If so, this is what it might look like, in his words:

SLOSH model predicts that a mid-strength Category 2 hurricane with 100-mph winds could drive a 15-20 foot storm surge to Manhattan, Queens, Kings, and up the Hudson River. JFK airport could be swamped, southern Manhattan would flood north to Canal Street, and a surge traveling westwards down Long Island Sound might breach the sea walls that protect La Guardia Airport. Many of the power plants that supply the city with electricity might be knocked out, or their docks to supply them with fuel destroyed. The more likely case of a Category 1 hurricane hitting at high tide would still be plenty dangerous, with waters reaching 8 - 12 feet above ground level in Lower Manhattan.

Storm surge for a Category 3 hurricane. Credit: NOAA's Storm Surge Interactive Risk Maps.

 
Here's a storm surge map for a Category 3 hurricane that I generated with NOAA's Interactive Risk Maps tool.

It's a good idea to use that tool to take a look at your own risks if you're anywhere along Irene's flight path.

Credit: Rhode Island National Guard.

Here you can see the storm surge damage from 1954's Hurricane Carol in Westerly, Rhode Island. Buildings in the center of the photo were floated off their foundations. Buildings in the lower portion were swept completely away and only slabs and driveways remained. 

Sea surface temperatures on 23 Aug 2011. Credit: NASA Earth Observatory.

   
To make matters worse, sea surface temperatures are running 1 to 3 degrees F above average between North Carolina and New York.

Since warmer waters make for a wetter storm, Irene will likely manifest as a superwet double whammy: wet from intense rainfall, and wet from intense storm surge.

Predicted rainfall from 25-31 August 2011. Credit: NOAA/NWS HPC.

    
This 5-day precipitation forecast forewarns Irene's real fury. Monster rainfall totals will likely lead to flooding of streams and rivers along much of the East Coast.

Hurricane Irene forecast path as of 2200 UTC 25 Aug 2011. Credit: NOAA.

   
Here's Irene's projected path as of 5pm EDT today.

Hurricane Irene at 2245 UTC 25 Aug 2011. Credit: NOAA/GOES Project Science.

  
And here's what the storm's looking like at 4:30pm EDT.

NEW VIEWS OF HURRICANE IRENE

Hurricane Irene has become a huge storm as of 2040 UTC, 24 Aug 2011, with hurricane-force winds extending 50 miles from the center, and tropical storm-force winds extending up to 205 miles from the center. Credit: NASA/GOES Project Science.

A stitched hemispherical view on 24 Aug 2011. You can see the low pressure systems to the north in Canada steering Irene. Credit: NASA/GOES Project Science.

Low and high pressure systems across North America influencing Irene's path and, ultimately, her landfall. Credit: GOES/SFSU.

Infrared image showing cloud tops at 20:45 UTC, 24 Aug 2011. The highest clouds are powerful bearers/drivers of wind and rain. Credit: NASA.

Sea surface tempertaures (Celsius) are a vital part of Hurricane Irene's fuel on the run north up the Gulf Stream. Water temperatures are 1-3�F warmer than average this year between North Carolina and New York, making Irene a wetter than average hurricane. Credit: NOAA.

A top-down view of rain intensities within Irene on 23 Aug 2011. Though Irene does not appear to have an eye in visible satellite imagery (the solid white center shows that it is still completely covered over with cloud), TRMM reveals an eye surrounded by a complete eyewall of varying rain intensities deep down under the cloud tops. The eyewall forms a complete circle in the rain field at the center of the image. The northeast corner of the eyewall contains an area of intense rain (darker red area), while the southern portion contains only light rain (shown in blue). Moderate rain (green areas) makes up the rest of the eyewall. The storm is still fairly asymmetrical, however, with most of the surrounding rain northeast of the center. Credit: NASA Earth Observatory. Images produced by Hal Pierce and caption by Steve Lang and Hal Pierce.

Taken at the same time as image above, shows a three dimensional view of Irene. Areas in red mark the tops of deep convection towers where precipitation-sized particles are being carried higher into the atmosphere by strong thunderstorms. These storms within a storm can intensify tropical cyclones and hurricanes by releasing large amounts of heat, known as latent heat, via condensation. This heat can intensify the hurricane�s circulation especially when released near its core. Credit: NASA Earth Observatory. Images produced by Hal Pierce and caption by Steve Lang and Hal Pierce.

Irene at 22:15 UTC, 24 Aug 2011. The low angle of the day's last visible light illuminates the highest cloud tops in spiral bands to the southeast, north, and far to the northeast of the storm's center. Credit: NOAA.