Bob Blog 23 May

Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the
patterned world.
Compiled Sunday 23 May

On 11 May the earth-to-moon distance was 406,512 km, the farthest apogee for
the year, however its perigee this month on 26 May is with a distance of
357,309km that's 69km closer than last month, and the second closest for the
whole year, and it occurs 9hr 12min before a full moon, whereas last month
the perigee was 11hr 52mins after a full moon. This means that the media
this week will be all a gosh and call it a supermoon. See
www.fourmilab.ch/earthview/pacalc.html for a lunar apogee /perigee
calculator. (PS: I also recommend his planetarium, Home Planet
www.fourmilab.ch/homeplanet, originally written pre-millennium for Windows
95 I still find it the best and smallest computer planetarium).
Anyway, when the perigee is within a day or so of a full or new moon the
gravitational pulls that drive the tides line up producing what are called
"king tides". The extra pull isn't much --think of the back-and-forth of the
tide as similar to a kid on the swing with one parent each side giving a
push proportional to the time of the month. When things line up best we get
the best swing.
These King tides have higher highs and lower lows so stronger ebbs and flows
and these can be dangerous.
NIWA (New Zealand Institute) have constructed a "Red Alert" calendar showing
which days have King tides (red) and which days are "carefree" (blue) See
niwa.co.nz/sites/niwa.co.nz/files/styles/full_screen_feature/public/VisRep20
21RedTides.jpg

Another factor affecting coastal inundation is storm surge. Isobars on the
weather map are given in hectoPascals, and each hPa below the norm of 1013
may lift the sea as much as 1cm. this is called the "inverse barometer
effect" or IB. Also deep lows and usually fringed by zones of strong winds ,
and strong onshore winds can pile the sea upwards along a coastline, causing
a "storm surge". This is explained further at
www.linz.govt.nz/sea/tides/introduction-tides/meteorological-effects-tides

There is a deep low off to the northeast of NZ So, with combined effect of
larger tides, strong on shore winds, and low pressure, there is no surprise
that there is a storm surge on the North Island east coast this week. See
www.facebook.com/watch/TheInformerMB/
And we can track this storm surge thanks to NIWA tide gauge at Whitianga
wharf thanks to Environment Waikato and NIWA (SS=total storm surge,
IB=Inverse barometer).
See
niwa.co.nz/our-science/coasts/tools-and-resources/sea-levels/whitianga-wharf

The Tropics
The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical
Cyclone Potential is from www.ssd.noaa.gov/PS/TROP/TCFP/index.html
During the past week Cyclone Tauktae damaged the West Coast of India and Ana
as named as the first cyclone of the North Atlantic season. Overnight
tonight the tropical depression in the Bay of Bengal is likely to be named
YAAS.
There are also some zones of potential development in the China Sea and east
of Philippines.

WEATHER ZONES

SPCZ=South Pacific Convergence zone.
The SPCZ is expected to be rather thin and weak, stretching from Solomon
Islands across norther Vanuatu to Fiji/Tonga.
A weak passing trough is expected southeast of French Polynesia.
Rain Accumulation next five days from windy.com

Subtropical ridge (STR)
HIGH up to 1034 over south of South Island on Monday is expected to travel
east along 45S and weaken.
Next High is expected to finally get east of Tasmania by Wednesday 2 June.

Aussie/Tasman/NZ troughs
Low has deepened to NE of NZ and is expected to stall and loop there, with a
squash on its south side, finally moving off on Thursday.
Then on Friday another Low is expected to form in the Tasman Sea and to
travel over North Island on Sat/Sun 29/30 May, followed for several days by
a SW flow over NZ.

Panama to Galapagos/Marquesas
Light winds for Panama. SW/S winds from 5North to Galapagos. As for going to
Marquesas, currents are better id go via north of Galapagos.
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If you would like more detail for your voyage, then check metbob.com to see
what I offer.
Or Facebook at /www.facebook.com/metbobnz/ Weathergram with graphics is at
metbob.wordpress.com (subscribe/unsubscribe at bottom).
Weathergram archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or txt 64277762212
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