Bob Blog 9 June 2019



Compiled Sun 09 June 2019

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.

Where’s the El Nino?

The state of the ENSO =almost an El Nino at times

The Atmosphere:

El Nino and La Nina are opposite ends of the swing of an identifiable tropical influence on our seasonal weather: the La Nina, caused by cooler than normal seas along the equatorial eastern pacific. shifts the subtropical ridge away from the equator, and the El Nino, with warmer than normal seas, draws the subtropical ridge closer to the equator. Their comings and goings can last several months, maybe over a year, and so their status can be used to help forecast the weather for the coming season.

ENSO = El Nino/Southern Oscillation. The main parameter we watch from the atmosphere is the Southern Oscillation Index SOI (30 day running mean) as it sums up the whole weather pattern over the South Pacific in one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin, in other words it counts the average number of isobars between them on the weather map. When the SOI is more than plus one (standard deviation from its mean) for more than a month we call it a LA NINA event, and when it stays more than minus-one we call it an EL NINO event.

Since February the SOI has been negative, and for a while in March was touching a weak El Nino. Since then it has weakened, but in the last week it is touching into El Nino again. If it continues as negative as this then the South Pacific may be in for weaker trade winds and more SW wind events than normal


Near El Nino conditions as seen at

(Note that in this graph on the vertical axis 10= 1 standard deviation)

The Ocean:

NINO3.4 is a region in the eastern equatorial Pacific Ocean that acts as a heat storage area during an El Nino or becomes cooler than normal during a La Nina. This plays with the heat budget of the atmosphere and thus with the weather patterns.

At the farmonline web site we can see the trend in the sea surface temperature in the NINO3.4 area. The diagram shows the weekly temperature anomalies since Jan 2016. Since then there has been several cool periods. Sea has warmed since May 2018 and touched El Nino territory late last year and in Feb/March 2019 and since then has been relaxing, Data missing for May and June. The ocean has not been in tandem with the atmosphere.


Near El Nino at times as seen at

The International Research Institute of the Climate Prediction Centre compiles data from several ENSO prediction models. The model predictions for the Nino 3.4 SST anomaly is that the seas should stay much the same for the next few months but may warm a little more between the coming October to January period. s


CPC/IRI predictions from

The latest SST anomaly map from shows lots of warm anomalies across the entire tropics, except for NW Australia and the Humboldt current off South America.


Sea surface temperatures across the Pacific on 6 June from


There are no cyclones at present, but there is potential off the central American west coast and about the south on India. The latest cyclone activity report is at and TCFP tropical Cyclone Formation Potential at




Weather Zones (see text) as expected Wednesday 00UTC showing isobars, winds, waves(magenta) STR, and SPCZ. Pink area = lightning likely (high CAPE)

SPCZ=South Pacific Convergence zone.

The SPCZ stretches from Solomons to Fiji and Tonga this week. A trough is expected to travel across Fiji and Tonga on Monday to Wednesday and then to travel off to the southeast.


Accumulated rainfall for next week from

Subtropical ridge (STR)

HIGH at 30S to north of NZ on Monday is expected to travel slowly east.

Next HIGH is expected to enter from Australia into Tasman Sea on Tuesday and slowly cross the Tasman Sea to ne north of NZ on Saturday.

Australia to Noumea

With the near southerly winds ahead of each of these Highs there is a brief opportunity for sailing from Australia to Noumea, departing Monday or Friday/Saturday.

A passing trough crossing the Tasman Sea on Tuesday and Wednesday may  impede a voyage from Noumea to Australia.

NZ to tropics:

Monday departure should be OK to go around the back side of the trough that is crossing Fiji and Tonga Monday to Wednesday, and trips to Tonga are able to avoid the larger swells from the Tasman Sea. Trough is expected to cross Northland on Tuesday night /early Wednesday, Stay put for that, but should be OK to depart in the SW flow that follows


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