** Reply to note from Murray H.

Mike Patterson had said -


> Curious about the kind of conditions that would drive a curlew 2000+
> mile off course? Have a look at the GOES9 photo from May 2, 1998.
>
>
> http://www.ncdc.noaa.gov/pub/data/goesbrowse/1998/g9ir02MAY199800.jpg

.. and then Murray wrote -

> Mike: I fear that you assume that all of us reading the Tweeters postings
> could access the www address. Would it be possible for you to give those of
> us who have "dinosaur" computers a general rundown, e.g. "wind from, etc.".
> (Have followed the Bristle-thighed Curlew reports with great interest but,
> sadly, haven't been able to do any chasing.) Am sure you've seen the other
> reports from Ocean Shores, WA and points north (from Patrick Sullivan
> today.) Tweeters is great but there are still a few of us out here who could
> use a little help.

I'll give you the best rundown I can, Murray. Mike is right that there was a
seasonally anomalous weather pattern present during early May north of Hawaii.
But as with all things weather-related this year, it all starts with El Nino...

Synopsis:

First a general summary of the winter weather pattern over the Pacific. There
are usually two streams of air prevalent over the Pacific during the winter -
the Maritime stream over northern sections and the Polar stream over the
southern sections. These are usually just referred to by the shorter forms as
the "northern" and "southern" streams. When El Nino was still gaining strength
during November and December, these two streams were "in phase", i.e. the
troughs and ridges lined up in each stream. This augments the strength of the
flow in each stream and we ended up with a high speed jet stream across the
N. Pacific. During these two months, a ridge of high pressure dominated along
the west coast of N. America (the so-called Pacific North America or PNA
pattern) bringing a strong flow of El Nino-warmed air to all the west coast.

As Californians can tell you, this pattern changed drastically in January.
Instead of a phased PNA pattern, it changed to a pronounced "split flow", in
which the energy flowing along the streams divided into two or more branches
instead of one consolidated one. And the one with the greatest energy was aimed
at California through most of January and February, ravaging that state with a
constant barrage of storms.

As El Nino peaked in March and April, the flow became more chaotic with a
greater variation in weather patterns as the two streams phased and split
several times.

Toward the last week of April, the energy started to be funnelled into the
southern stream again as a huge split took shape in the flow over the western
Gulf of Alaska. A deep upper low centre began to form near 31N, 150W by the 27th
of April, about 600 nautical miles NNE of Hawaii. An upstream surface low
pressure system caught in the westerlies was forced southward upon entering the
Gulf of Alaska and deepened explosively due to the influence of both the
presence of the upper low and its trajectory over the abnormally warm waters.

One such surface low pressure system entering the Gulf April 28 followed this
trajectory and eventually bottomed out at around 985 millibars near 38N, 135W
May 1. The surface low and upper low then began moving in tandem northeastward
toward the California coast. By May 2, the day the satellite photo in Mike's
post was taken, the still strong low pressure centre began weakening off the
north-central California coast as the warm air occluded out of the system and it
became a "cold low".

During this period, a strong cold front associated with the cold air flowing
southward in the wake of the surface low pressure centre was moving steadily
southward. This cold front reached the Hawaiian Islands about 2200 hours UTC on
May 1 accompanied by strong north winds and lots of showers. See the following
URL for those with Web access to see this cold front just a few hours before
landfall at Hawaii:

http://www.ncdc.noaa.gov/pub/data/goesbrowse/1998/g9vs01MAY199818.jpg

Northerly surface winds to the north of the cold front were averaging 20-30
knots, with the core of fastest wind speeds attaining 40-50 knots on the west
side of the surface low centre farther northeast. Over the next five days, the
cold low centre meandered off the California coast and gradually dissipated. The
winds to the north of Hawaii remained out of the north but weakened steadily.

On May 7-9, another much weaker cold front swept southward down the west coast
accompanied by a few showers and gusty onshore winds. On May 8, another cold
front entered the Gulf of Alaska and turned sharply southward off the west
coast. By the morning of May 12, this front arced south and westward from Los
Angeles. This front was not as strong as the first one but the winds were still
fairly stiff out of the north when it reached Hawaii May 14.

Discussion:

Most of the Polynesian wintering Bristle-thighed Curlews _Numenius tahitiensis_
depart for their western Alaskan breeding grounds in late April-early May. Birds
leaving Hawaii for Alaska during this period would have experienced brisk head
winds and frequent showers. The first sighting of two curlews (according to
Tweeters) was made May 8 at Ocean Shores, one week after the passage of the
strong cold front across Hawaii.

It is probable that these curlews were deflected northeastward by the cold
front. Note that this is a 50-80 degree deflection from a straight-line path to
Alaska depending on whether the birds first made landfall in Washington or
California. I feel that two scenarios are possible: 1)The birds intercepted the
advancing cold front north of Hawaii on either April 30 or May 1. The birds
would have experienced strong north winds and frequent showers. After fighting
the head winds for a while, the birds turned to the NE towad the west coast;
2) The birds departed Hawaii after the blustery north winds hit the Islands and
for some reason headed NE rather than NNW to Alaska. The first sounds the most
plausible to me.

Do not let anybody tell you that this is not a significant event. Indeed, the
arrival of other Bristle-thighed Curlews along the coast subsequent to the first
two suggests that either a wayward flock dispersed when it made landfall on the
coast, or that there was another wave following the first.

The cynics among us may purport that these birds could have been transported by
some crazed pineaple-addled seaman. However, I believe that a bout with a feisty
Mother Nature is more likely.

- Jack













--------------
Jack Bowling
Prince George, BC
jbowling at direct.ca