Powerful “Medicane” hits France
by Dr. Jeff Masters in a Wunderblog repost
The most powerful storm to affect the Bering Sea coast of Alaska in 37 years is pounding Alaska’s west coast and Eastern Siberia with hurricane-force winds, a destructive storm surge up to 7 feet high, waves up to 35 feet high, and blinding snow. Tin City on the west coast of Alaska north of Nome recorded sustained winds of 70 mph, gusting to 81 mph, at 1:55 am local time this morning, and hurricane-force winds are likely affecting much of the open waters of the Bering Sea.
Figure 1. Visible satellite image of the Bering Sea superstorm at 7 pm EST November 8, 2011. Image credit: National Weather Service.
A storm surge of 6 feet hit Nome, Alaska this morning, pushed inland by sustained winds that reached 45 mph, gusting to 61 mph. A even higher storm surge is predicted for this evening (Figure 3.) The last time Nome, Alaska saw a storm this strong was November 11 – 12 1974, when the city experienced sustained winds of 46 mph with gusts to 69 mph, a pressure that bottomed out at 969 mb, and a storm surge of 13 feet that pushed beach driftwood above the previous high storm tide mark set in 1913. The center of today’s storm moved ashore over eastern Siberia near 12 UTC with a central pressure of 945 mb. The storm has likely peaked in strength, and will gradually weaken as it moves northeast into the Arctic.
Figure 2. Observed storm surge at Nome, Alaska (green line). MLLW = Mean Lower Low Water, the water level at the lowest tide of the month. Image credit: NOAA Tides and Currents.
Figure 3. Predicted storm surge (yellow-brown line) for Nome, Alaska for today’s Bering Sea storm. The black line is the predicted storm tide–the water level reached as a result of the storm surge and the natural tidal cycle. Tidal range at Nome is normally less than 2 feet between low tide and high tide (green line.) MAT = Maximum Astronomical Tide, MLLW = Mean Lower Low Water. Image credit: National Weather Service.
Figure 4. Predicted storm surge for today’s storm, as forecast by the Ocean Prediction Center’s Extratropical Storm Surge Model. Image credit: NOAA Environmental Visualization Lab.
Climate change likely to worsen erosion along the Alaska coast
Arctic sea ice was at its 2nd lowest extent on record during October 2011, according to the National Snow and Ice data Center. Much of the missing ice this fall is along the Bering Sea coast of Alaska, where today’s massive storm is hitting. When sea ice disappears, coastlines become more susceptible to battering waves. This is particularly common during the fall season, not only because sea ice extent is usually at its minimum, but fall is when storms tend to be stronger with higher storm surges. Recent coastal destruction has already forced residents of the Alaskan town of Shishmaref to vote to abandon their village. More than half the residents of the nearby village of Kivalina (population 400) were forced to evacuate in September 2007, when 25 – 40 mph winds drove a four foot storm surge into the town. The U.S. Army Corps of Engineers completed a $16 million sea wall and shore fortifications in 2009 to protect the town, and Kivalina is trusting these protections during today’s storm; no evacuations occurred. As of 11 am EST today, Kivalina has seen top sustained winds of 51 mph, gusting to 71 mph.
Figure 5. Kivalina, Alaska in 2005. Note how the homes on the right side of the image are perched precariously close to the ocean, due to erosion that has eaten away the shore. Image credit: Millie Hawley.
As sea ice continues to decrease in coming years, leaving more ocean surface exposed to air, more moisture and heat will be available to power storms. As I discussed in detail in my post, The future of intense winters storms, multiple studies have documented a significant increase in the number of intense extratropical cyclones with central pressures below 970 or 980 mb over the North Pacific and Arctic in recent decades. Computer climate models predict predict a future with fewer total winter storms, but a greater number of intense storms; up to twelve additional intense Northern Hemisphere cold-season extratropical storms per year are expected by the end of the century if we continue to follow our current path of emissions of greenhouse gases. These stronger storms will bringer higher winds and higher storm surges to coastal areas of Alaska and the Arctic over the remainder of the 21st century, resulting in increased erosion and flooding of low-lying areas. Contributing to the erosion will be sea level rise. Kivalina, which lies on a narrow barrier island in the Chukchi Sea, has been losing up to 8 feet of shore each year due to erosion, and the long-term survival of the island is in serious doubt. Plans have been drawn up by the Army Corps of Engineers to relocate the city to the mainland, but finding funding for the $100 – $400 million dollar move has been problematic. The city of Kivalina and a federally recognized tribe, the Alaska Native Village of Kivalina, sued Exxon Mobil Corporation, eight other oil companies, 14 power companies, and one coal company in a lawsuit filed in federal court on February 26, 2008, claiming that the large amounts of greenhouse gases these companies are responsible for contribute to global warming that threatens the community’s existence. The lawsuit estimates the cost of relocation at $400 million.
Figure 6. The Kivalina sea wall as seen in 2007. Image credit: City of Kivalina.
Figure 7. The projected change in intense wintertime extratropical storms with central pressures < 970 mb for the Northern Hemisphere under various emission scenarios. Storms counted occur poleward of 30°N during the 120-day season beginning November 15. A future with relatively low emissions of greenhouse gases (B1 scenario, blue line) is expected to result in an additional four intense extratropical storms per year, while up to twelve additional intense storms per year can be expected in a future with high emissions (red and black lines). Humanity is currently on a high emissions track. Figure was adapted from Lambert and Fyfe (2006), and was taken from Weather and Climate Extremes in a Changing Climate, a 2009 report from the U.S. Global Change Research Program (USGCRP).
Powerful “Medicane” hits France
A hybrid low pressure system pounded Southeast France yesterday, bringing heavy rains, hurricane-force winds gusts, and significant coastal flooding. The storm began over the weekend as an extratropical storm named “Rolf”, but then stalled out over the relatively warm waters of the Mediterranean, acquiring tropical characteristics. Heavy thunderstorms similar in intensity to what one would get in a tropical storm built up, and Rolf developed sustained winds above tropical storm force. These sort of hybrid extratropical/tropical storms that form over waters colder than 22°C are sometimes called “Medicanes”, and can cause substantial damage. Rolf brought heavy rains in excess of 400 mm (15.7″) over the past 4 days to the department of Var, north of Toulon. A wind gust of 95 mph was recorded at 21 UTC November 8 at Porquerolles Island, south of the city of Toulon. French radar shows heavy rains from Rolf are continuing to affect Southeast France and the island of Corsica. Water temperatures off the south coast of France are near 17°C (63°F), far below the 26°C threshold usually needed to sustain a tropical storm.
— Dr. Jeff Masters is the co-founder of the Weather Underground. This post was originally published at the Wunderblog.
In any earlier post, Masters explained why global warming could lead to hurricanes in the Mediterranean, but they “should be rare and relatively short-lived”:
According to research published by Gaertner et al. (2007), an increase in ocean temperatures of 3°C in the Mediterranean by the end of the century could lead to hurricanes forming there. Miguel Angel Gaertner of the University of Castilla-La Mancha in Toledo, Spain, ran 9 different climate models with resolutions of about 50 km and found that some (but not all) of the models simulated hurricanes in the Mediterranean in September by the end of the century, when ocean temperature could reach 30°C.
Though the Mediterranean may start seeing hurricanes by the end of the century, these storms should be rare and relatively short-lived for three reasons:
1) The Mediterranean is quite far north and is subject to strong wind shear from jet stream activity.
2) The waters are shallow, and have relatively low heat content. There is no deep warm water current like the Gulf Stream.
3) The Mediterranean has a lot of large islands and peninsulas poking into it, increasing the chances that a tropical storm would weaken when it encountered land.