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Super Extra-tropical Storms; Alaska and Extra-tropical Record Low Barometric

By: Christopher C. Burt , 8:39 PM GMT on November 10, 2011

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


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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13. bfearn
5:12 PM GMT on December 30, 2015
When I was a kid, I'm 70 now, I talked with a neighbor who was a retired clipper ship sailor. He had a barometer recording that was off the bottom of the paper chart, 28", in the India Ocean. Must have been quite a ride in a sailing ship.
Member Since: December 31, 1969 Posts: Comments:
12. Snowfire
3:11 PM GMT on November 18, 2011
I was told during a visit to Alaska in 1985 that a storm (polar low?) had passed over Dutch Harbor in February of that year, producing a gust of 176 mph (151 kt).

I have also read in a weather book (which I no longer have, alas) that a barometric reading of 26.94" (912 mb)occurred during a severe thunderstorm in St. Louis, MO.

I have been unable to corroborate either of these stories.
Member Since: December 31, 1969 Posts: Comments:
10. Christopher C. Burt , Weather Historian
5:33 AM GMT on November 14, 2011
Quoting BaltimoreBrian:
Too bad all the sea ice around Antarctica makes deploying buoys there impossible. What kind of pressure records are kept in the Antarctic Peninsula?


Southern Hemisphere records are spotty at best. The lowest measurement reading for such that I'm aware of is 933 mb (27.59") at Hadley Bay, Antarctica on Aug. 11, 1994.

Records for isobar synoptics only go back to 1974, and no one, to my knowledge, has bothered yet to do an investigation into this particular feature (lowest pressure reading in Antarctica region). So the Hadley Bay 'record' is probably not that reliable.

Chris
Member Since: December 31, 1969 Posts: Comments:
9. Christopher C. Burt , Weather Historian
5:13 AM GMT on November 14, 2011
Quoting hungurdiskar:
The lowest pressure recorded in Iceland: Vestmannaeyjar 2 December 1929 920 hPa. A link in Icelandic - you should be able to read the figures.

http://www.vedur.is/vedur/frodleikur/greinar/nr/1 056

This storm (hurricane) caused extensive damage in Iceland.

Another case missing from the list:
Vestmannaeyjar 3 January 1933 923.9 hPa - almost as low in Reykjavik. The center of this low was very flat at landfall in Iceland so probably the central pressure had probably been lower before landfall.

Readings below 930 hPa are very rare in Iceland.

A buoy recorded 920 hPa in the 1986 case mentioned in the main blog text. It was programmed to disregard lower readings. Pressure readings were resumed after a few hours with blanks - above 920. I presume that the central pressure went down to 914 hPa.

But thank you for the very valuable effort of record collecting and the interesting blogs.


Excellent information 'hungurdiskar' contributor! This is an exciting update and much appreciated. Few people seem to pay attention to records like these, so I (and Stephen Burt) will review your information with enthusiasm!

Thanks again

Chris
Member Since: December 31, 1969 Posts: Comments:
8. BaltimoreBrian
1:28 AM GMT on November 14, 2011
I read something similar about the 1993 storm. That the buoy they used to calculate that pressure disregarded pressures below 925 mb. But they interpolated using the speed and direction of the wind to estimate the gradient and the low center did go over the buoy. What I read was that the pressure was interpolated to be 912/913 mb. The pressure was below 925 mb for 13 hours at that buoy. That is probably the longest duration below 925 mb anywhere. Maybe Typhoon Tip could have done it but I don't know how fast Tip was moving when the 870 mb reading was taken.

Quoting hungurdiskar:
The lowest pressure recorded in Iceland: Vestmannaeyjar 2 December 1929 920 hPa. A link in Icelandic - you should be able to read the figures.

http://www.vedur.is/vedur/frodleikur/greinar/nr/1 056

This storm (hurricane) caused extensive damage in Iceland.

Another case missing from the list:
Vestmannaeyjar 3 January 1933 923.9 hPa - almost as low in Reykjavik. The center of this low was very flat at landfall in Iceland so probably the central pressure had probably been lower before landfall.

Readings below 930 hPa are very rare in Iceland.

A buoy recorded 920 hPa in the 1986 case mentioned in the main blog text. It was programmed to disregard lower readings. Pressure readings were resumed after a few hours with blanks - above 920. I presume that the central pressure went down to 914 hPa.

But thank you for the very valuable effort of record collecting and the interesting blogs.
Member Since: December 31, 1969 Posts: Comments:
7. hungurdiskar
1:21 AM GMT on November 14, 2011
The lowest pressure recorded in Iceland: Vestmannaeyjar 2 December 1929 920 hPa. A link in Icelandic - you should be able to read the figures.

http://www.vedur.is/vedur/frodleikur/greinar/nr/1 056

This storm (hurricane) caused extensive damage in Iceland.

Another case missing from the list:
Vestmannaeyjar 3 January 1933 923.9 hPa - almost as low in Reykjavik. The center of this low was very flat at landfall in Iceland so probably the central pressure had probably been lower before landfall.

Readings below 930 hPa are very rare in Iceland.

A buoy recorded 920 hPa in the 1986 case mentioned in the main blog text. It was programmed to disregard lower readings. Pressure readings were resumed after a few hours with blanks - above 920. I presume that the central pressure went down to 914 hPa.

But thank you for the very valuable effort of record collecting and the interesting blogs.
Member Since: December 31, 1969 Posts: Comments:
6. Christopher C. Burt , Weather Historian
6:29 AM GMT on November 12, 2011
Quoting Wyote:
I worked on board The MV Viceroy during that October 1977 storm. We were tied up in Dutch Harbor at the time and it was quite the blow. I never realized how many vessels were in the area until the warnings went out and literally hundreds of boats came into that double sheltered bay. Along with a couple of Coast Guard cutters, we're all lashed together with tire bumpers between us.

Even in that sheltered harbor, the sea was rocking enough to make a lot of people seasick. I remember going up to the to the bridge area and looking at the barometer. The thing was pegged at 27.49. It didn't go any lower. On the windward side of the island of Unalaska, in an area called Captain's Bay, the word was the winds were clocked at 210 mph. As I recall, the storm whacked us for a good three days.

I live in Wyoming now, and although the wind is infamous here, it's nothing compared to that.

Thanks for your terrific blog, Christopher.


Thanks for this! Please see my updated blog entry with an interesting report from Steve Gregory about the 1977 storm.
Member Since: December 31, 1969 Posts: Comments:
5. Wyote
6:08 AM GMT on November 12, 2011
I worked on board the MV Viceroy during that October 1977 storm. We were tied up in Dutch Harbor at the time and it was quite the blow. I never realized how many vessels were in the area until the warnings went out and literally hundreds of boats came into that double sheltered bay. Along with a couple of Coast Guard cutters, we're all lashed together with tire bumpers between us.

Even in that sheltered harbor, the sea was rocking enough to make a lot of people seasick. I remember going up to the bridge area and looking at the barometer. The thing was pegged at 27.49. It didn't go any lower. On the windward side of the island of Unalaska, in an area called Captain's Bay, the word was the winds were clocked at 210 mph. As I recall, the storm whacked us for a good three days.

I live in Wyoming now, and although the wind is infamous here, it's nothing compared to that.

Thanks for your terrific blog, Christopher.
Member Since: December 31, 1969 Posts: Comments:
4. BaltimoreBrian
9:41 PM GMT on November 11, 2011
Too bad all the sea ice around Antarctica makes deploying buoys there impossible. What kind of pressure records are kept in the Antarctic Peninsula?
Member Since: December 31, 1969 Posts: Comments:
1. rod2635
1:47 AM GMT on November 11, 2011
Thanks so much for this information. With the recent Alaskan storm I was really curious about all time intensities. To see pressures below 28.00 is remarkable. To see so many in the 27.50 range and below in the Cat3/4 range is stunning. The storm off of Scotland at 26.96 is astonishing. One is often lured into the misconception that low central pressures are the province of tropical systems. Your information shows that other dynamics can produce equally powerful systems, often even more so when the extent of their wind fields is taken into account.
Member Since: December 31, 1969 Posts: Comments:

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About weatherhistorian

Christopher C. Burt is the author of 'Extreme Weather; A Guide and Record Book'. He studied meteorology at the Univ. of Wisconsin-Madison.

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