Bob Blog



Compiled Sun 15 April 2018

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.


IRIS: There were still convective squalls in the remains of IRIS in the Coral sea until last Thursday, about four weeks after it started.

KENI: Tropical cyclone KENI travelled over Kadavu on Tuesday 10 April, and then went southeast out of the tropics. As it left the tropics, KENI was captured by the jetstream belonging to an approaching upper trough. This ripped the upper part of the tropical feature to bits, but the surface low wasn’t affected much, as evidenced by (modelled) isobars around the centre. This is shown in an animation I took using Windy, looking at the EC model.


To see this, visit , entitled KENI and the Jets. Courtesy of Windy website

This animation also shows the squally trough that crossed North Island on Tuesday 10 April and how clouds in this feature were able to bring twisting winds and tornadoes to New Plymouth, and, a few hours later, were able to bring jetstream like-winds downwards as damaging downbursts that fanned Auckland on Tuesday evening.

Here’s the weather story for Auckland airport from the passage of that front:


Courtesy of Windy website.

Yes, the peak gust was over 80 knots and the gale lasted around 14 hours.

My email server was knocked offline for a day. Anyone who sent me an email last Wednesday was sent a bounce message that may have said things like “domain doesn’t exist” or even “has been blacklisted”. Charming, I don’t think.

Tropical Outlook for remainder of the month:

The next MJO (or pulse of enhanced convection) is still building in the Indian Ocean and now looks like it will reach Western Pacific towards the end of April. By then the nominal cyclone season will be ending. And until then it looks as if the South Pacific should be in a period of quieter convection. So, the signs are now pointing to an end of this cyclone season in the South Pacific (but North Australia may get one more opportunity towards end of the month).

Now that cruising sailors are preparing for their voyages to the tropics, if you wish to join an organised rally, well the Down Under crowd are in full swing arranging the GO EAST Cruisers rally from the Gold Coast (starting around 14 May) to New Caledonia. For more info see and the Island Cruising New Zealand are organising a rally from Opua to Tonga, but registration for this is now full. If you’d like to join the waiting list then see



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

SPCZ=South Pacific Convergence zone.

The SPCZ is weaker and thinner than last week, and is expected to stretch from eastern Solomon Islands, to Wallis/Futuna and between Samoa and Tonga to Austral islands.

There is still an “extra convergence zone” around 5 to 8S from SW of Galapagos around 100W to northeast of the Marquesas around 120W.


Accumulated rainfall for next week from

Subtropical ridge (STR)

HIGH between Fiji and NZ tonight is travelling away to east along 30S and should fade away by Wednesday.

Next HIGH is expected to form in central Tasman Sea on Tuesday and Wednesday and then travel northeast across northern North Island by the 21/22 weekend. This system should flatten the large swells that are in the Tasman Sea at the start of the week, so that there may be a reasonable opportunity for some trans-Tasman sailing.

And, now that these Highs are travelling east along 30 to 35S, this offers a reasonable opportunity for vessels seeking an opportunity to sail from NZ to French Polynesia.

Around Tasman Sea

Some deep lows are expected to be travelling east along 50S in the Southern Ocean, so there should be an enhanced westerly flow across central and southern NZ this week. The Southern Alps are consequently expected to get more rain than the SPCZ.

Panama to Galapagos /Marquesas

For sailing from Panama, there is expected to be some moderate northerly winds on Tuesday/Wednesday/Thursday. After that the winds are likely to switch to light southwesterly. So, if you are waiting to go, take this opportunity.

As from getting from Galapagos to Marquesas this week, first motor sail to around 5S 94W (may also find a tail current), then can sail direct, but that “extra” convergence zone continues to straddle 5 to 6S from about 100W to 120W. Something to avoid.


If you would like more detail for your voyage, then check to see what I offer.

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Published by metbob

Pattern and Chaos

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