Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 1:57 PM GMT on October 27, 2009
El Niño conditions have strengthened in recent weeks, crossing the threshold from "weak" to "moderate", according to data compiled by NOAA's Climate Prediction Center. NOAA defines "moderate" El Niño conditions as existing when sea surface temperature (SST) departure from average in the equatorial Eastern Pacific (the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region") warms above 1.0°C. According to the latest time-series plot of "Niña 3.4 region" SSTs (Figure 1), we crossed that threshold last week. Monthly average SSTs will have to remain above 1.0°C for five consecutive months in order for this to be considered a "moderate" El Niño event. The ongoing intensification of El Niño could have major impacts on this winter's weather.
Figure 1. Departure of sea surface temperature (SST) from average for the past two years along the equatorial Eastern Pacific (the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region"). Moderate strength El Niño conditions occur when the Niña 3.4 anomaly exceeds 1.0°C, which occurred last week (red arrow). Weak El Niño conditions (Niña 3.4 anomaly between 0.5 - 1.0°C) were present from early June to mid-October. Image credit: NOAA Climate Prediction Center.
The intensification of El Niño is due to a combination of events in the ocean and the atmosphere. In the ocean, a slow-moving wave of water more than 5°C (9°F) warmer than average is progressing from west to east along the Equator (Figure 2). This wave, known as a "Kelvin" wave, is focused at a depth of 150 meters, but also affects surface waters. The Kelvin wave was at 175W on October 1, and is now near 140W, so it is traveling east at about 4 mph (100 miles/day). At the ocean surface, a burst of west-to-east winds near the Date Line has weakened the trade winds (Figure 3), which blow the opposite direction--east to west. The trade winds have weakened by 1 - 2 m/s over the past few weeks, allowing the Kelvin wave to push warm water eastward towards South America. The result of this interplay between ocean and air is an intensification of El Niño conditions from weak to moderate.
Figure 2. Animation of the ocean temperatures (top) and departure of ocean temperatures from average (bottom) as a function of depth along the Equator in the equatorial Eastern Pacific. The left side of the image is near Australia, and the right side is near the coast of South America. At the beginning frame in the bottom image on October 5, an ocean Kelvin wave is apparent at a depth of 150 meters, where the ocean temperature is up to 3°C above average (yellow colors). The wave travels eastwards at about 100 miles/day. By the final frame (October 25), the Kelvin wave has warmed to a temperature 5°C above average (orange colors). The Kelvin wave is helping to push the warm water at the surface to the east, as seen in the progression of the red and orange colors eastwards in the top image. I constructed the animation using the free ImageMagick package on a Linux machine, using data plotted up from the NOAA's Tropical Atmospheric Ocean (TAO) project web page.
Figure 3. Top: Sea Surface temperatures (colors) along the Equator between New Guinea and South America, with surface wind vectors overlaid. Note that there is a burst of westerly winds near the Date Line, 180W. This westerly wind burst is weakening the trade winds, which blow the opposite direction, east-to-west, over the ocean between the Date Line and the coast of South America. Bottom: Departure of wind speed from average along the Equator shows the effect of the westerly wind burst, which has weakened the trade winds at the surface by 1 - 2 m/s along a large swath of ocean near the Equator. The reduction in trade winds allows the warm water to the west to slosh eastwards, intensifying El Niño. Image credit: NOAA's Tropical Atmospheric Ocean (TAO) project web page.
Quiet in the Atlantic
There are no threat areas in the Atlantic to discuss, and none of the computer models is calling for tropical storm formation over the next seven days. This should be a quiet week in the region we need to be most concerned about for a late-season hurricane, the Western Caribbean. Wind shear is forecast to be marginal for tropical storm development this week, and most of the Caribbean is very dry at present. One possible area of concern early next week may be near Bermuda, where the models indicate a large non-tropical low may cut off from the jet stream 6 - 7 days from now. This low could potentially remain over warm waters long enough to acquire tropical characteristics and become Subtropical Storm Ida. Such a storm would only be a threat to Bermuda.
Philippines under the gun yet again
The typhoon-weary Philippine Islands have a new worry--Tropical Storm Mirinae is strengthening quickly east of the islands, and could be a typhoon later today. Latest infrared satellite loops show a large and expanding region of intense thunderstorms with very cold cloud tops, with well-developed spiral banding and excellent upper-level outflow developing. Wind shear is a moderate 15 knots, and the ocean temperatures are very warm, 29°C. These warm waters extend to great depth, and the Tropical Cyclone Heat Potential (TCHP) is 80 - 100 kJ/cm^2 along Mirinae's entire path to the Philippines. Values of TCHP in excess of 90 kJ/cm^2 are frequently associated with rapid intensification, and I expect Mirinae will be a major Category 3 or higher typhoon by Thursday. Mirinae is expected to track westward and hit the Philippines' Luzon Island on Saturday. With wind shear expected to remain in the low to moderate range, the models fairly united about a westward track over the Philippines, and plenty of ocean heat to feed off, the odds certainly favor a strike by Mirinae at Category 1 or higher strength on hard-hit Luzon.
Figure 2. Tropical Storm Mirinae, as it passed north of the Guam radar station last night.
Statisticians reject global cooling
An interesting exercise was conducted by the Associated Press (AP), who gave global average temperature data for the past 130 years to a group of independent statisticians, and told them to analyze the data without telling them what the data represented. These experts concluded that the data showed a distinct decades-long upward trend in the numbers, and no significant drop in the past ten years. This is not too surprising, since no scientific studies in peer-reviewed scientific journals have supported the idea that the globe is cooling. The AP exercise was the lead story in this morning's on-line version of the MSNBC news. Dr. Ricky Rood's climate change blog has an interest analysis of global warming and cooling trends, and how natural variability over years or decades can mask long-term trends. With El Niño cranking up to moderate levels heading into 2010, there's at least a 50/50 chance that year will end up beating 2005/1998 as the warmest year on record, putting the "global cooling" hype to rest for a few years.
Second Annual Portlight Honor Walk
Saturday, December 5, 2009 or Sunday, December 6, 2009
A nationwide grassroots event to raise funds for and awareness of Portlight's ongoing efforts specifically aimed at providing Christmas presents for kids and families devastated by the recent Atlanta floods, South Carolina wildfires, American Samoa tsunami, and other disasters that may occur.
Un-served, underserved and forgotten people are depending on us.
We need one hundred people across the country to commit to walking one mile on this day, and to raise at least $300.00 in sponsorship from friends, family, co-workers, neighbors, etc. Participants can choose where to walk--it can be the park, the mall the neighborhood--anywhere you choose. The first 100 participants to raise at least $300 will receive a commemorative T-Shirt.
To register, simply e-mail your intention to participate at firstname.lastname@example.org
Check the Portlight featured Weather Underground Blog regularly for updates!
The Honor Walk Sponsor Form available here will help you keep track of funds and pledges:
Portlight's Paul Timmons on the Barometer Bob Show Thursday night
Portlight's Paul Timmons will be appearing live this Thursday at 8pm EDT on the Barometer Bob Show, an Internet radio show that I have appeared on several times in the past. Be sure to catch his discussion of how Portlight got started, where they're going, and what's new!
I'll have a new post on Wednesday, when I'll discuss how the recent intensification of El Niño may affect winter in the U.S.
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