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Bob McDavitt's ideas for sailing weather around the South pacific

16 April 2017

Bob Blog 16 April 2017, Happy Easter

WEATHERGRAM
YOTREPS
Compiled Sun 16 April 2017

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.

It's Easter again, time for new beginnings.

The track of Cyclone COOK
Cyclone COOK did a fair amount of damage to New Zealand, but not as much as BOLA (March 1988) or GISELLE (April 1968), maybe as much, or slightly more than Cyclone BERNIE (April 1982) or FERGUS (Dec 1996).
MetService have written a blog giving a summary of the track of Cyclone COOK at blog.metservice.com/CycloneCookSummary

It shows the track that was issued on Tuesday as cyclone COOK approached landfall, and the one issued on Friday, with the blue cone showing the spread of uncertainty. These maps show that COOK did not deepen as quickly or as much as the global models calculated, and took a track slightly, but significantly, further east. Nonetheless, it was a formidable feature, with gusts to 209 km/hr at White Island and at least 100 km/hr at Whakatane, and waves over 12 metres recoded at a Bay of Plenty wave buoy. It made landfall near Whakatane in the Bay of Plenty where the barometer bottomed out at 980hPa.

A power failure affected the data coming in from the Bay of Plenty as COOK approached, but using the "Last 48 hours" feature available to registered members at predictwind.com, we can fine-tune where COOK made landfall.

Data from White Island shows that soon after 3pm on Thursday 13 April there was a wind peak with gusts to 113kt/ 209km/hr, then at around 5:30pm the easterly winds turning northerly then counter-clockwise to southerly. We can surmise that the centre started off somewhat west of White Island on approach, and ended up somewhat east of White Island on egress.

At Hicks Bay around 6pm Thursday, wind went from easterly to northerly and gusted to over 60 knots /118 km/hr, so the centre of COOK made landfall west of Hicks Bay.

And Whakatane data shows the peak wind speed just after 6pm Thursday, with wind then turning counter-clockwise from southerly to easterly. This would be on the approach of the centre and sadly we don't have data to see if the wind continued to swing counter-clockwise (in which case landfall was west of Whakatane) or changed to clockwise (in which case landfall was east of Whakatane).

The Tropics
Tropical depression 19F has been slow-moving in the Tonga /Southern Cooks area for most of April so far and is now expected to fade away and maybe track to the west over the next few days. After that it looks as though the South Pacific cyclone season may be spent.
However action is already starting in the Northern Hemisphere, with 01B MAARUTHA in the Bay of Bengal heading for Myanmar (Burma) and a tropical depression (Two) forming near Palau that may move towards Philippines later this week.See ruc.noaa.gov/tracks/

Rain from last week, compared with previous week, at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif shows the track of cyclone COOK and MAARUTHA. South Pacific convergence zone is weakening. The ITCZ is returning to normal and the convergence zone between Tuvalu and Galapagos is still there, but now with gaps.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is weak and mainly over northern Coral Sea this week. There is still a convergence zone between Tuvalu and Galapagos and another near Southern cooks/ French Polynesia, but these zones are slowly weakening. The tropical accumulated rainfall for next week may be seen at windyty.com

Subtropical ridge (STR)
Large High well to east of NZ is intensifying and moving slowly NE, and may reach over 1030hPa on Monday and Tuesday UTC near 33S 148W. There is a squash zone of enhanced easterly winds on north side of this, with large swells. Avoid this squash zone.
Another High is expected to reach over 1030hPa in central Tasman sea from Tuesday to Sunday UTC, and then cross central NZ on Sun/Mon 23/24 April. There is likely to be a squash zone of strong SE winds in the Coral sea. Take care.

Departing NZ for the tropics:
Looks good for departure over next few days, but after Thursday 20 April not so good as there may be easterly swells over 3 metres to north of NZ.

Australia to New Caledonia: Too much easterly this week.

Mexico to Marquesas:
The next strong Tehuantepec NE blast of wind near 95W is expected around 24 to 25 April, and there is a minor one from 19 to 21 April.
Further north, it should be useful north to NW flow for departure until 19 April, and then lighter variable winds until 25 April.
There is likely to be just light winds between 15 and 12N, the NE trade winds should be useful from 12N to 10N---then light wind are likely from 10N to Equator. Perhaps more wind if you go a bit further west of the rhumb line. Maybe aim for equator 130W.
Intertropical convergence zone is spread out between 10N and 5N. And there is still another convergence zone near 5S, but that may ease over next few weeks. South of that zone there should be useful easterly trade winds for sailing to Marquesas.

Panama to Galapagos
OK northerly winds if you depart by 17 April local, otherwise just light SW winds around Panama.
Main convection is likely between 8N and 4N.

Galapagos to Marquesas
There is now a zone of light winds on the direct path, and a convergence zone between 5s and 9S, so need to go as far as 10S maybe 11S to avoid that. Maybe go to waypoints 7S 100W then 11S 135W then direct. The pattern is changing and may well be different in a week or so, so get updates.

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