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A Rare Event: Heavy Rains in Northwest U.S. From an Ex-Hurricane

By: Dr. Jeff Masters, 4:03 PM GMT on October 28, 2014

The heavy rains and strong gusty winds that began affecting the Northwest U.S. and Western Canadian coasts on Monday evening are due to a truly rare event: the remains of a Hawaiian hurricane getting slung into the coast as part of a large extratropical storm. The moisture is from Hurricane Ana, which, after making an extended tour just offshore of the Hawaiian islands last week, died on Sunday afternoon over the Pacific about 1,300 miles west of the California/Oregon border--unusually far to the northeast for a tropical cyclone to make it. In fact, there is only one other case since 1949 where the remnants of a hurricane that formed in the Eastern or Central Pacific has had a significant impact on the Pacific Northwest or Western Canada--an unnamed 1975 storm that maintained hurricane strength to 46.8°N (the latitude of the Oregon/Washington border.) That storm was the only hurricane on record to make it farther to the northeast of Hawaii than Ana, which maintained hurricane strength to a latitude of 36.3°N--approximately the latitude of Monterey, California. Even the notorious Hurricane Iniki, which hit Kauai as a Category 4 storm on September 11, 1992, only made it to 35°N latitude as a hurricane. Fortunately, ex-Ana's rains of 2 - 6" are not expected to cause serious flooding in the Pacific Northwest. The only Flood Watch for the storm is over Western Washington, where heavy rains in the Olympic Mountains may be enough to drive rivers close to flood stage.

Figure 1. MODIS satellite image of the extratropical storm containing the remains of Hurricane Ana impacting the Northwest U.S. and Western Canadian coasts on Monday afternoon, October 27, 2014. Image credit: NASA.

Figure 2. Tracks of all Central Pacific tropical depressions, tropical storms, and hurricanes to make it far to the north of the Hawaiian Islands (at least 34°N latitude.) Image credit: NOAA.

Figure 3. Departure of Sea Surface Temperature (SST) from average along the track of Hurricane Ana as of October 27, 2014. A large area of SSTs 2 - 3°F above average to the north of Hawaii allowed Ana to maintain hurricane strength much farther north than is usual in the Central Pacific. Warmer than normal ocean temperatures during the summer and fall of 2014 in the Central Pacific allowed a record three hurricanes--Iselle, Julio, and Ana--to come within 300 miles of the Hawaiian Islands. Image credit: Remote Sensing Systems.

Remnants of typhoons occasionally affect Pacific Northwest
There have been a number of Western Pacific typhoons that have died north of Hawaii and gone on to bring heavy rain to western Canada; this happens about twice per decade. According to wunderground's weather historian Christopher C. Burt, the most destructive storm in the history of the Pacific Northwest formed from the remnants of a Western Pacific typhoon. That storm was the notorious "Big Blow" or Columbus Day Storm of October 12, 1962 that killed 46 and caused $1.9 billion in damage (2014 dollars). The Western Pacific's Typhoon Freda, a Category 3 storm that formed near Wake Island west of the Date Line, became an extratropical storm with 45 mph winds shortly after crossing the Date Line, and went on to intensify into a 969 mb monster off the coast of Oregon that brought wind gusts as high as 145 mph to the coast that terrible October day in 1962.

Figure 3. The track of the Columbus Day storm from its inception as a typhoon on October 3 to the time it made landfall as a powerful extra-tropical storm on Vancouver Island, Canada on October 13th. The storm became extra-tropical in the West Pacific on October 9th. USWB chart reproduced in Weatherwise magazine’s December 1962 issue.

Figure 4. The Big Blow topples the Campbell Hall Tower on the campus of Western Oregon State College in Monmouth near Salem where 90 mph wind gusts were measured. Photo by Wes Luchau.

Remnants of Hanna bringing heavy rain to Central America
Tropical Storm Hanna dissipated on Monday evening over northern Nicaragua, just 14 hours after springing into life less than 50 miles off of the coast. Visible satellite images on Tuesday morning showed that the remnants of Hanna were over Northern Honduras and the Western Caribbean, and these heavy thunderstorms will move westwards over Belize, Northern Guatemala, and the Yucatan Peninsula Tuesday afternoon and into Wednesday, bringing areas of 3 - 5" of rain. The center of ex-Hanna was located just inland from the northern coast of Honduras on Tuesday morning, and was being tracked as Invest 96L by NHC.

Figure 5. Latest satellite image of 95L.

Invest 95L near the northern Lesser Antilles a possible threat to Bermuda
An area of disturbed weather (95L) associated with a tropical wave interacting with an upper level trough of low pressure is near the northern Lesser Antilles Islands, and is headed northwestward to west-northwestward at 10 to 15 mph. Satellite loops show that 95L has a modest amount of heavy thunderstorm activity that is poorly organized. Wind shear is high, 15 - 25 knots, and water vapor satellite images show that 95L has dry air to its north and west that is likely interfering with development. Sea Surface Temperatures (SSTs) are warm, about 29°C. The 8 am EDT Tuesday run of the SHIPS model predicted that wind shear would remain high for the next five days, limiting the prospects for development. None of our three reliable models for predicting tropical cyclone genesis predict development of 95L over the next five days. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day development odds of 20% and 30%, respectively. The only land area at risk from 95L is Bermuda.

Figure 6. MODIS satellite image of Tropical Cyclone Nilofar in the Arabian Sea on Tuesday morning, October 28, 2014. At the time, Nilofar was an intensifying Category 4 storm with 130 mph winds. Image credit: NASA.

Tropical Cyclone Nilofar the 3rd strongest Arabian Sea storm on record
In the Arabian Sea between India and Africa, powerful Category 4 Cyclone Nilofar is putting on an impressive bout of rapid intensification as it heads northwards at 10 mph towards Pakistan. With wind shear a light 5 - 10 knots, excellent upper-level outflow, and very warm ocean temperatures about 1°C above average: 28 - 29°C (82 - 84°F), Nilofar may be able to continue intensifying until Wednesday morning, when very dry air from the deserts of the Middle East, combined with high wind shear, should be able to weaken the storm. Nilofar is expected to recurve to the northeast later this week, and the 00Z Tuesday runs of the UKMET and European models predicted the shear and dry air would be able to destroy Nilofar before it could make landfall. The GFS model keeps Nilofar as a weakening tropical storm at landfall near the Pakistan/India border around 00 UTC Saturday. Heavy rains are likely to be the most significant threat from the storm.

Intense hurricanes are rare in the Arabian Sea, due to the basin's small size, the interference of the summer monsoon, and the frequent presence of dry air and dust from the Arabian Peninsula. Nilofar's 130 mph sustained winds make it the third strongest tropical cyclone ever recorded in the Arabian Sea, behind the 165 mph winds of Category 5 Cyclone Gonu of 2007, which devastated Oman, and the 145 mph winds of Category 4 Cyclone Phet of 2010, which also did heavy damage in Oman. Fourth place is held jointly by the 2001 India Cyclone 01A and Very Severe Cyclonic Storm ARB 01 (02A) of 1999, which were Category 3 storms with 125 mph winds.

Eastern Pacific disturbance near tropical depression status
A well-organized area of disturbed weather in the Eastern Pacific a few hundred miles southwest of the Mexico/Guatemala border (Invest 93E) is close to tropical depression status. Our top three models for predicting tropical cyclone genesis all develop the system, and in their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development near 100%. The storm's heaviest rains will remain well offshore from Mexico over the next five days.

Jeff Masters


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