Bob blog

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 4 May 2025

A review of last month's weather

Here is a link to a YouTube clip giving an animated loop of the
isobars and streamlines in the South Pacific for the last month at
youtu.be/M72SdfJhSnk

In Mid-April Cyclone TAM formed near Vanuatu and travelled south into
the Tasman Sea where it was held in place for several days by a HIGH
east of NZ, affecting NZ on the approach of Easter.

Then at the end of the month another LOW from the Tasman Sea
explosively deepened near Cook Strait bringing floods to Christchurch
area and damaging winds to Wellington

The 500hPa heights and anomalies shows last month's typical ridge
/trough pattern, with the Highs showing either wave 2 to 3

Sea Surface temperature anomalies as at 2 May
from psl.noaa.gov/map/clim/sst.shtml
show that The Galapagos area is now showing some warm anomalies.
And there is a cold anomaly along the Canadian east coast.
Around 85percent of the globe is showing warm anomalies.

From http://www.psl.noaa.gov/map/images/fnl/slp_30b.fnl.html

A ridge has turned into a trough in the Tasman Sea, else just small
differences from last month.

Pressure anomalies for past month shows deep anomalous lows in Tasman
Sea and mid-South Atlantic, and a switch from trough to ridge over
USA.

The 1010 isobar has retreated off Australia.
The northern 1015 line has moved north across Australia, but south in
the Tasman Sea.
The southern 1015 line is in much the same position.

TROPICS
A quiet week for tropical cyclones

WEATHER ZONES
Rain accumulation this week from Windy.com shows well defined SPCZ and
blobs of rain with L2 and L4
The wind accumulation shows a squash zone between 20 and 25S from near
Vanuatu to Southern Cooks. It also shows strong northerly winds near
NZ with L2.

LOWS and HIGHS

Low L1, the remains of the low that affected wellington and
Christchurch last Thursday, is travelling off to the east

HIGH H1 travelling east across central NZ next few days is expected to
form a squash zone of strong east to SE wind on its northern side
between 20 and 25S. Avoid.

Low 2 is expected to form over Vanuatu area late in the week and might
travel as a trough towards Northland this weekend as low L3 travels
east across southern NZ.

Since L2 might turn the winds between NZ and Tonga to be from NE late
this week it may be more comfortable to wait until early next week or
when this threat passes away before departing Northland for the
tropics.

now south of Southern Cooks is moving slowly SE.  Associated trough is
expected travel from Niue to Southern Cross this week, and the
southerly swells on its backside are expected to reach French
Polynesia late in the week.

HIGH H2 is expected to move into Tasman Sea by end of this week.

And there is expected to be a low L4 forming south of Tahiti by end of
the week.

Gulf of Panama:  Maybe some useful northerly winds from 8 to 15May,
else light winds.
Some light winds next few days then useful NE winds after Tuesday.
Showery.
6N to 2N: Showery, often westerly or SW winds and a sea drifting to
east
2N to Galapagos: Winds from between SW and S and a sea drifting to the
NW.

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