WunderBlog Archive » Weather Extremes
Category 6 has moved! See the latest from Dr. Jeff Masters and Bob Henson here.Super Extra-tropical Storms; Alaska and Extra-tropical Record Low Barometric
Super Extra-tropical Storms; Alaska and Extra-tropical Record Low Barometric Pressures
One of the most powerful storms to strike Alaska in recent years has churned across the Bering Sea with hurricane-force winds and sea waves some 40-feet high. See Jeff Masters blog for details on this storm. My blog here is a brief historical re-cap of past storms of similar magnitude (including one just last April in Alaska) and record low pressure readings for extra-tropical storms.
Surface chart of the recent storm at its most intense when it bottomed out at 943 mb (27.85”) late on November 8th local time.
Alaska’s Strongest Extra-tropical Storm on Record: October 25-26, 1977
The most powerful storm, at least in terms of depth of pressure, to affect Alaska in modern history was that of October 25-26, 1977. Dutch Harbor, on the Aleutian Island of Unalaska, recorded a minimum pressure of 925 mb (27.31”) on the evening of October 25th. Winds gusted to 130 mph at Adak, also in the Aleutian Islands. Adak reported a continuous 12-hour period with wind gusts of 110mph+ between 1800Z Oct. 25 and 0600Z Oct. 26. Enhanced infrared radar imagery indicated a closed ‘eye wall’ with this storm. Wave heights of 35 feet on top of swell heights of 60 feet produced significant wave heights of 72 feet according to NWS analysis and ship reports. The analysis speculated that there was the potential for waves as high as 120 feet, although nothing of this magnitude was actually observed. The cyclone had its origins, as is often the case with powerful Alaskan storms, as a West Pacific typhoon.
Hand-drawn weather maps used to be an art! Here are two views of the October 1977 storm; the full version and a detail of the surface analysis for late evening October 25, 1977 when Alaska’s strongest storm in history deepened to 925 mb (27.31”) over Dutch Harbor on the Aleutian Island of Unalaska. Chart drawn by and supplied to me by Steve Gregory who worked with the Ocean Routes Company (now WNI) in Alaska at the time. Steve just sent me this very informative email (in part correcting my mistake in the original post concerning his affiliation with the NWS:
"I didn't work for the NWS, I worked for Oceanroutes (now WNI) when in AK doing site specific forecasts for 7 exploratory drilling rigs located about 6 miles offshore of Cape Yagataga along the south central coast. That location was something else. When I first started, I worked as an observer on one of the rigs (2 weeks on, 2 weeks off) and when storm systems approached, winds would increase to about 3 times what one would normally expect based on the observed pressure gradient, and winds were always out of the East, perpendicular to the isobars. No one really knew why - but we suspected it had to do with a glacier located just to our northeast. A rough rule of thumb was to use the pressure difference between Yakatut and Middleton Island - with every millibar difference equal to 5 Kts. 60Kt winds were very common - averaging 1 or 2 times /week on average. You haven't lived until you've been out on the ocean with 80mph winds and 30 foot waves.
One final comment. You will find that storms with NWS analyzed pressures of 948mb (or lower) occur quite frequently in the Gulf of Alaska. Must average at least 5 such storms every year, with 1 or 2 of them getting into the 930's. But these mega-storms attract little attention because there is no major affect on any populated areas (although aircraft landing in ANC can experience true, severe turbulence on approach through Turnagain Arm. I've never really had the time to check, but I suspect a careful analysis would show pressures in the 920's."
Other Powerful Alaskan Storms
The highest wind gust yet measured in Alaska was 159 mph at the isolated settlement of Attu on December 7, 1950. Attu is located on the westernmost Aleutian Island of the same name, some 1000 miles west of Anchorage.
The state’s highest sustained one-minute wind speed of 93 mph was recorded at Kotzebue during a storm on February 25, 1951.
Although the current storm has received quite a bit of publicity, its minimum pressure of 943 mb is still shy of the strongest storm so far observed this year which swept over the Aleutian Islands and into the Bering Sea on April 6th with a minimum pressure of 939 mb (27.73”). Cold Bay reported a maximum wind gust of 91 mph.
Surface map of the April 7, 2011 storm that although stronger than the recent November storm (939 mb vs. 943 mb) was less destructive since it shied further away from the Bering Sea Alaskan coastline.
In October 2004 and again in September 2005 two large storms with central pressures of 941mb produced a storm surge of almost 10.45 feet at Nome beaching boats and damaging the town’s waterfront where an unofficial wind gust of 83mph was recorded. The ferocity of both storms led then NWS Fairbanks’s Office Lead Fore caster, Rick Thoman, to comment, “Storms that affect Alaska are far, far bigger than hurricanes. Hurricanes are tiny compared to great storms that take up a quarter of the Bering Sea.” REF: Alaska Science Forum Article #1774: ‘No Hurricanes in Alaska but…’ by Ned Rozell, October 27, 2005.
A ten-foot storm surge deposited boats along the shoreline of Nome’s Snake River in September 2005. Nome’s greatest storm surge occurred during a storm in November 1974 when waters rose 13 feet above normal. Photo by Ned Rozell.
Cause of Alaskan Super Storms
The reason for the amazing intensity of some of the extra-tropical storms that swipe the Aleutians and the Bering Sea is that the low-pressure centers tap into relatively mild, moist sub-topical air off the coasts of Japan (sometimes the remnants of typhoons) and cold dry air centered over Eastern Siberia; somewhat in the same fashion that low pressure systems sometime ‘bomb out’ along the Eastern Seaboard of the United States after entraining, in their case, Gulf Stream moisture and Canadian cold, dry air.
Comparison to Atlantic Extra-tropical Storms
Amazing as the pressure readings observed during some Alaskan super storms, they still cannot quite compare (yet!) to the strongest low-pressure storms that form during the winter months in the North Atlantic.
In January 1993 a series of intense low-pressure systems passed near Scotland’s Shetland Islands and over the North Sea. On January 5th one such storm caused the super oil tanker Braer to be blown onto a rocky shoal on one the Shetland Islands. A stronger storm on January 10-11th caused the ship to break apart and release its contents resulting in a massive oil spill.
The oil tanker ‘Braer’ founders on the rocky shoreline of the Shetland Islands on January 5, 1993. Photographer unknown.
The storm that caused the Braer to break up had a central pressure of 913 mb (26.96”), the lowest sea-level adjusted barometric pressure ever observed on the earth’s surface, aside from tropical storms and tornadoes of course.
An infrared satellite image of the North Atlantic Storm of January 11, 1993 at 0600Z when it deepened into the strongest extra-tropical cyclone ever observed on earth with a central pressure of 913 mb (26.96”). Satellite image from EUMETSAT Meteosat-4.
Other Atlantic storms have also recorded barometric pressures lower than the Dutch Harbor figure, including 920.2 mb (27.17”) by the ship Uyir while she sailed southeast of Greenland on December 15, 1986. The British Met. Office calculated that the central pressure of the storm, which was centered some distance southeast of the ship, was 916 mb (27.05”). British weather historian, Stephen Burt has also made note of other remarkable low-pressure readings from the North Atlantic:
921.1 mb (27.20”) on Feb. 5, 1870 measured by the ship Neier at 49°N 26°W (another ship in the area measured 925.5 mb)
924 mb (27.28”) on Feb. 4, 1824 at Reykjavik, Iceland (the lowest on land measured pressure in the North Atlantic)
925.5 mb (27.33”) on Dec. 4, 1929 by the SS Westpool somewhere in the Atlantic (exact location unknown)
925.6 mb (27.33”) on Jan. 26, 1884 at Ochtertyre, Perthshire, U.K. (the lowest pressure recorded on land in the U.K.)
For comparison’s sake, the lowest pressure measured on land during an extra-tropical storm in the United States (aside from Alaska) was 952 mb 28.10” at Bridgehampton, New York (Long Island) on March 1 during, the Great Billy Sunday Snowstorm.
On the West Coast the lowest pressure measured on land was 962 mb (28.40”) at Quillayute, Washington on December 1, 1987. However, a ship near the mouth of the Umpqua River in Oregon measured a pressure of 955 mb (28.20”) during the Great Storm King of Jan.9, 1880.
KUDOS: Thanks to Steve Gregory for the map of the Alaskan storm of 1977 and related information. Thanks also to Stephen Burt for list of North Atlantic pressure records.
Christopher C. Burt
Weather Historian
One of the most powerful storms to strike Alaska in recent years has churned across the Bering Sea with hurricane-force winds and sea waves some 40-feet high. See Jeff Masters blog for details on this storm. My blog here is a brief historical re-cap of past storms of similar magnitude (including one just last April in Alaska) and record low pressure readings for extra-tropical storms.
Surface chart of the recent storm at its most intense when it bottomed out at 943 mb (27.85”) late on November 8th local time.
Alaska’s Strongest Extra-tropical Storm on Record: October 25-26, 1977
The most powerful storm, at least in terms of depth of pressure, to affect Alaska in modern history was that of October 25-26, 1977. Dutch Harbor, on the Aleutian Island of Unalaska, recorded a minimum pressure of 925 mb (27.31”) on the evening of October 25th. Winds gusted to 130 mph at Adak, also in the Aleutian Islands. Adak reported a continuous 12-hour period with wind gusts of 110mph+ between 1800Z Oct. 25 and 0600Z Oct. 26. Enhanced infrared radar imagery indicated a closed ‘eye wall’ with this storm. Wave heights of 35 feet on top of swell heights of 60 feet produced significant wave heights of 72 feet according to NWS analysis and ship reports. The analysis speculated that there was the potential for waves as high as 120 feet, although nothing of this magnitude was actually observed. The cyclone had its origins, as is often the case with powerful Alaskan storms, as a West Pacific typhoon.
Hand-drawn weather maps used to be an art! Here are two views of the October 1977 storm; the full version and a detail of the surface analysis for late evening October 25, 1977 when Alaska’s strongest storm in history deepened to 925 mb (27.31”) over Dutch Harbor on the Aleutian Island of Unalaska. Chart drawn by and supplied to me by Steve Gregory who worked with the Ocean Routes Company (now WNI) in Alaska at the time. Steve just sent me this very informative email (in part correcting my mistake in the original post concerning his affiliation with the NWS:
"I didn't work for the NWS, I worked for Oceanroutes (now WNI) when in AK doing site specific forecasts for 7 exploratory drilling rigs located about 6 miles offshore of Cape Yagataga along the south central coast. That location was something else. When I first started, I worked as an observer on one of the rigs (2 weeks on, 2 weeks off) and when storm systems approached, winds would increase to about 3 times what one would normally expect based on the observed pressure gradient, and winds were always out of the East, perpendicular to the isobars. No one really knew why - but we suspected it had to do with a glacier located just to our northeast. A rough rule of thumb was to use the pressure difference between Yakatut and Middleton Island - with every millibar difference equal to 5 Kts. 60Kt winds were very common - averaging 1 or 2 times /week on average. You haven't lived until you've been out on the ocean with 80mph winds and 30 foot waves.
One final comment. You will find that storms with NWS analyzed pressures of 948mb (or lower) occur quite frequently in the Gulf of Alaska. Must average at least 5 such storms every year, with 1 or 2 of them getting into the 930's. But these mega-storms attract little attention because there is no major affect on any populated areas (although aircraft landing in ANC can experience true, severe turbulence on approach through Turnagain Arm. I've never really had the time to check, but I suspect a careful analysis would show pressures in the 920's."
Other Powerful Alaskan Storms
The highest wind gust yet measured in Alaska was 159 mph at the isolated settlement of Attu on December 7, 1950. Attu is located on the westernmost Aleutian Island of the same name, some 1000 miles west of Anchorage.
The state’s highest sustained one-minute wind speed of 93 mph was recorded at Kotzebue during a storm on February 25, 1951.
Although the current storm has received quite a bit of publicity, its minimum pressure of 943 mb is still shy of the strongest storm so far observed this year which swept over the Aleutian Islands and into the Bering Sea on April 6th with a minimum pressure of 939 mb (27.73”). Cold Bay reported a maximum wind gust of 91 mph.
Surface map of the April 7, 2011 storm that although stronger than the recent November storm (939 mb vs. 943 mb) was less destructive since it shied further away from the Bering Sea Alaskan coastline.
In October 2004 and again in September 2005 two large storms with central pressures of 941mb produced a storm surge of almost 10.45 feet at Nome beaching boats and damaging the town’s waterfront where an unofficial wind gust of 83mph was recorded. The ferocity of both storms led then NWS Fairbanks’s Office Lead Fore caster, Rick Thoman, to comment, “Storms that affect Alaska are far, far bigger than hurricanes. Hurricanes are tiny compared to great storms that take up a quarter of the Bering Sea.” REF: Alaska Science Forum Article #1774: ‘No Hurricanes in Alaska but…’ by Ned Rozell, October 27, 2005.
A ten-foot storm surge deposited boats along the shoreline of Nome’s Snake River in September 2005. Nome’s greatest storm surge occurred during a storm in November 1974 when waters rose 13 feet above normal. Photo by Ned Rozell.
Cause of Alaskan Super Storms
The reason for the amazing intensity of some of the extra-tropical storms that swipe the Aleutians and the Bering Sea is that the low-pressure centers tap into relatively mild, moist sub-topical air off the coasts of Japan (sometimes the remnants of typhoons) and cold dry air centered over Eastern Siberia; somewhat in the same fashion that low pressure systems sometime ‘bomb out’ along the Eastern Seaboard of the United States after entraining, in their case, Gulf Stream moisture and Canadian cold, dry air.
Comparison to Atlantic Extra-tropical Storms
Amazing as the pressure readings observed during some Alaskan super storms, they still cannot quite compare (yet!) to the strongest low-pressure storms that form during the winter months in the North Atlantic.
In January 1993 a series of intense low-pressure systems passed near Scotland’s Shetland Islands and over the North Sea. On January 5th one such storm caused the super oil tanker Braer to be blown onto a rocky shoal on one the Shetland Islands. A stronger storm on January 10-11th caused the ship to break apart and release its contents resulting in a massive oil spill.
The oil tanker ‘Braer’ founders on the rocky shoreline of the Shetland Islands on January 5, 1993. Photographer unknown.
The storm that caused the Braer to break up had a central pressure of 913 mb (26.96”), the lowest sea-level adjusted barometric pressure ever observed on the earth’s surface, aside from tropical storms and tornadoes of course.
An infrared satellite image of the North Atlantic Storm of January 11, 1993 at 0600Z when it deepened into the strongest extra-tropical cyclone ever observed on earth with a central pressure of 913 mb (26.96”). Satellite image from EUMETSAT Meteosat-4.
Other Atlantic storms have also recorded barometric pressures lower than the Dutch Harbor figure, including 920.2 mb (27.17”) by the ship Uyir while she sailed southeast of Greenland on December 15, 1986. The British Met. Office calculated that the central pressure of the storm, which was centered some distance southeast of the ship, was 916 mb (27.05”). British weather historian, Stephen Burt has also made note of other remarkable low-pressure readings from the North Atlantic:
921.1 mb (27.20”) on Feb. 5, 1870 measured by the ship Neier at 49°N 26°W (another ship in the area measured 925.5 mb)
924 mb (27.28”) on Feb. 4, 1824 at Reykjavik, Iceland (the lowest on land measured pressure in the North Atlantic)
925.5 mb (27.33”) on Dec. 4, 1929 by the SS Westpool somewhere in the Atlantic (exact location unknown)
925.6 mb (27.33”) on Jan. 26, 1884 at Ochtertyre, Perthshire, U.K. (the lowest pressure recorded on land in the U.K.)
For comparison’s sake, the lowest pressure measured on land during an extra-tropical storm in the United States (aside from Alaska) was 952 mb 28.10” at Bridgehampton, New York (Long Island) on March 1 during, the Great Billy Sunday Snowstorm.
On the West Coast the lowest pressure measured on land was 962 mb (28.40”) at Quillayute, Washington on December 1, 1987. However, a ship near the mouth of the Umpqua River in Oregon measured a pressure of 955 mb (28.20”) during the Great Storm King of Jan.9, 1880.
KUDOS: Thanks to Steve Gregory for the map of the Alaskan storm of 1977 and related information. Thanks also to Stephen Burt for list of North Atlantic pressure records.
Christopher C. Burt
Weather Historian
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.