Bobgram

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 18 May 2025

The QBO (stratospheric Quasi Biennial Oscillation)
Last week in my weathergram I showed that our recent South pacific
cyclone season was one of the quietest ever. Maybe the QBO can partly
explain this
The Quasi-Biennial Oscillation (QBO) is a natural climate pattern
that causes a shift in the direction of the equatorial stratospheric
winds, switching between easterly and westerly winds. These winds are
read twice daily by radiosondes released from Singapore. This
oscillation, with an average period of about 28 months, can have an
impact on weather patterns and is considered a valuable component of
long-range weather forecasting.

From acd-ext.gsfc.nasa.gov/Data_services/met/qbo/qbo.html
During the last cyclone season the equatorial stratosphere had
westerly winds. more than normal, and there was a slightly lower
troposphere than normal. These factors make it harder for tropical
cyclones to develop.
TROPICS

This week the monsoon is advancing onto southern Indian (blue lines
below)
From mausam.imd.gov.in/imd_latest/contents/monsoon.php

WEATHER ZONE

Wind and rain accumulation this week from Windy.com
The wind accumulation shows a windy zone attached to that "Eastie"
which briefly forms off the New South Wales coast, and a lot of
southerly winds onto Chatham Island east of NZ, on the back end of L1
There is also zone of enhanced trade winds mainly between 20 and 25S
south to south of Fiji.

The rain accumulation also shows a rain band associated with "Eastie"
and a rather uniform SPCZ north of Fiji
LOWS and HIGHS
Low L1 and its associated troughs has got east of New Zealand today
and Monday and is expected to travel steadily eastwards this week.

HIGH H1 is over Bass strait tonight and expected to take its time
travelling east across the Tasman Sea then cross central NZ next
weekend. By then it will have a weak squash zone in the trade winds on
its north side. GFS has a trough/low forming near Minerva reef
Mon/Tue 26-27 May but other models disagree. Watch that space and be
prepared to brace accordingly.

Gulf of Panama: Just light winds Health current going to SW.
6N to 2N: Not as showery as last week South to SW winds. Variable
currents
2N to Galapagos: Winds from S/SE and sea drifting to the WNW.
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Contact is bob@metbob.com or text 64277762212.
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