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Volume 16 Issue 1 Jan 2023
Pacific Atmospheric Rivers: A Sign of Change
Kyle Petroziello, Meteorologist

The Pacific Ocean Basin currently resides in a La Niña Climate Pattern. La Niña is referred to as the “cold phase” of the ENSO (El Niño/Southern Oscillation) cycle. It occurs when the sea-surface temperatures of the Equatorial Pacific are below average. ENSO is an oscillating warming and cooling pattern change of the tropical Pacific Ocean that affects global circulation.

In a normal La Niña winter, there are two main weather features over the Northeast Pacific that drive the usual weather pattern. A semi-permanent blocking high pressure is found between Hawaii and the Aleutian Islands. The Polar Jet Stream takes on a wave-like characteristic as it flows north of this high, then south into the Pacific Northwest U.S. while remaining amplified. This setup produces occasional gales that track similarly to the jet stream and remain north of the ridge before tracking SW’ward into the Pacific Northwest U.S., while the East-Central Pacific remains quieter.

La Niña is expected to gradually weaken over the next several months, with these dominant features losing their influence. This is right on par for the expected ENSO cycle. The historical interval between La Niña and its warmer water counterpart – El Niño – occur every 2 to 7 years, and we are now approaching two and a half years of a prevailing La Niña (26 of the last 28 months). A shift to an ENSO-neutral pattern (the happy medium between these two) is expected to develop into this upcoming spring.

A glaring indicator of this soon-to-be changing of the guard has been the unprecedented Northeast Pacific weather pattern for much this past month. This break in the pattern has instead seen persistent upper-air troughing across the Gulf of Alaska while the Polar Jet Stream retreats far to the north and the strong Pacific Jet Stream has taken over. It has become an immensely straight-line zonal feature, extending across the entire Pacific from Japan to California along 30N-40N.

This change caused January 2023 to feature an unprecedented series of successive Atmospheric Rivers flowing into the U.S. West Coast, with historic rainfall. Atmospheric Rivers are essentially narrow columns of water vapor (moisture) that originate over the tropics and flow like rivers aloft over long distances. Consecutive strong gales, under the influence of the persistent Pacific Jet Stream, have propagated E’ward in a conga-line fashion across the S’rn mid-latitudes of the Pacific, only a few days apart. These strong gales pull moisture from the tropics as Atmospheric Rivers, producing a firehose-like release of tropical moisture upon the U.S. West Coast. A notable example of this was the notorious “Bomb Cyclone” within the first week of January that approached California, depicted below.

Figure 1 shows impressive Visible Satellite Imagery of the January 04th Bomb Cyclone with notations

 

Figure 2 shows Winds, Seas, and Pressure associated with the January 04th Bomb Cyclone (source: www.seaweather.net)

In Figure 1, the moisture plume transported water nearly 2,000 nautical miles from the Hawaiian Islands to just offshore California at the time. In Figure 2, the Winds, Seas, and Pressure map from SeaWeather of the same system indicated sustained winds over 50 knots and swells in excess of 10 meters produced just south of the center of the gale. These are overlaid in the notated visible satellite imagery in Figure 1 as well.

The more S’rn tracks of these gales within the Pacific mid-latitudes have allowed large swells to propagate much further south, through the entire Baja Peninsula and towards the west coast of Mexico at times, than usual for a La Niña winter. This has posed considerable challenges for potential Baja and West Coast transits this past month. Though, this month of January is considered an extreme pattern and these strong S’rn gale tracks are unlikely to persist as frequently in the many months ahead. However, it is an indicator of a more active Northeast Pacific climate pattern expected through the next several months as La Niña phases out, sustaining challenges for N’ward transits into the warmer spring and summer months.

WRI meteorologists are ready to assist you with any West Coast hops in this active pattern. Our SeaWeather website (www.seaweather.net) also offers many features to help examine impacts from this changing pattern on your potential voyage in the months ahead.

2022 Atlantic Basin Hurricane Season
Jason Caterina, Meteorologist

The 2022 Atlantic Basin Hurricane season was not as active as in recent years, and fairly average by a number of metrics, but notable nonetheless for several interesting reasons.
 
Strictly by the numbers, it seemed to be rather unremarkable.  There were 14 named storms, eight of those strengthened into hurricanes, and two became major hurricanes (category three or higher). Based on the 30-year average from 1991-2021, this is roughly normal with the average being 14 named storms, seven hurricanes, and three major hurricanes.  So, on the surface, the 2022 Atlantic hurricane season did not seem all that out of the ordinary.  However, looking a little closer, some interesting notes come to light.

•    The first cyclone of the season, Tropical Storm Alex, formed on June 05th with the last cyclone of the season, Hurricane Nicole, dissipating on November 11th.  With Alex not forming until June 05th, this became the first season since 2014 not to have a pre-season named storm. 

•    Two storms formed on the same day, July 01st and one of the two, Tropical Storm Bonnie, was the first cyclone to survive crossing from the Atlantic to the Pacific basin since Hurricane Otto in 2016.  Not since 1996 has more than one storm crossed between Atlantic and Pacific intact during a single season. 

•    After these two simultaneous storms, there was a lull for nearly two months before the next tropical cyclone formed.  This made the 2022 Atlantic hurricane season the first since 1997 in which no tropical cyclones formed during the month of August, and the first season on record to do so during a La Niña year. 

•    With three named storms forming during November, the 2022 season tied with the 2001 season for the most named storms to form in the month of November. In November, more named storms formed than in all of July and August. 

•    Despite the lull and relatively normal number of named storms, the 2022 Atlantic hurricane season wound up being the 3rd costliest season on record with over $120 billion dollars in damage estimated, mostly thanks to Hurricane Ian, with damages estimated at $113 billion alone.


 Figure 1:  The above graph shows the ACE Index for the years 2010-2022 compared to the mean value of the ACE Index between 1951-2020.

The ACE Index, a metric used to express the energy released by a tropical cyclone during its lifetime, for the entire season was 95.1 which is near normal on the scale, the first year since 2010 to be near normal on the index.  By comparison, 2016-2021 were all considered above normal to extremely active while 2013-2015 were below normal.  

WRI’s team of Meteorologists were on the job, working diligently to keep our clients safe, providing accurate and timely updates 24 hours a day and seven days a week.  WRI also offers complimentary tropical surveillance to our clients while using WRI and for a couple of weeks after the voyage.  This service is continuous for Sea Weather subscribers. 

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