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 Sunday 21 April 2024

SOI is changing.

It's now official. The El Nino of last year is now over and we are in
neutral territory. El Nino is the name given to the period when sea
surface temperatures over the eastern equatorial Pacific are above
normal. A good measure of this is the Nino 3.4 index. The graph shown
here from the Bureau of Meteorology, Australia has the Nino 3.4
measurements and calculated trends from an ensemble of computer
models. Neutral conditions are in the offering for winter and spring,
and there may be a swing to La Nina next summer,

The SOI or Southern Oscillation index comes directly from the isobars
found on a weather map. It measures the difference in barometric
pressure readings between Tahiti and Darwin, basically giving an idea
of the strength of the trade winds.

It has been in El Nino (negative) territory since last May, and has
relaxed to neutral in the past month.

Climate experts say that the relaxing of the El Nino help them
determine if the recent unprecedented high temperatures worldwide have
been due to accelerated climate change or not. NOAA predicts there is
an 85% chance the El Niño warmth will be gone sometime before June,
while Australia's Bureau of Meteorology says the tropical Pacific sea
surface already "cooled substantially" during mid April. The absence
of that heat will reduce the vertical wind shear that typically
squashes hurricane and tropical storm development in the Atlantic
Basin, possibly leading to a very active hurricane season.

During the "neutral" period for the next few months the weather is
likely to swing from one pattern to another, allowing variety as each
pattern gets to "play" for a short time. I call this "weather Jazz"


TROPICS
It is a quiet time with no named cyclones. There is a weak MJO
crossing the Pacific longitudes this week, and a slight increase is
cyclone potential around New Caledonia.

WEATHER ZONES
It's a busy weather map this week with four lows: 2 in the tropics and
2 in the mid- latitudes.

The South Pacific Convergence zone is active between New Caledonia and
Southern Cooks, and is breeding tropical lows, as is typical during an
MJO pulse. Low L1 is expected to form south of Fiji on Monday and then
travel east and fade away over Niue area by mid-week. Low L2 is
currently in the Coral Sea and expected to deepen over New Caledonia
mid-week and then travel SE to the east of NZ by weekend. Avoid.

HIGHS and LOWS

Low 3 travelled over northern NZ in past few days and is moving off to
the SE.

HIGH H1 is in the Tasman Sea and expected to travel across northern NZ
mid-week and then move off to the east along 35 to 40 South.,
shepherding L2 towards SE of NZ by weekend.

Low L4 is expected to cross Tasmania on Wednesday and its associated
trough should cross NZ on Thursday and Friday and connect with L2 then
to north of NZ. Avoid.

If planning a Trans Tasman trip then work in with H1.

If planning to sail from NZ to tropics wait until after L2.

Panama to Marquesas: Northerly winds for starters. Doldrums between
6N and 2N with erratic winds and squally showers.

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