Bob Blog

WEATHERGRAM

YOTREPS

Issued 25 January 2015

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

The Ocean: The extra heat that has been stored in the eastern equatorial Pacific Ocean is now decreasing and no longer pointing to an El Nino episode.

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Ocean Heat index showing a relaxing in the El Nino trend as seen at as shown at http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=nino34&p=weekly

The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin. It has been negative since July and dived below -10 (Australian units) for much of September, and again for a week in November, then relaxed in early December, and has been up and down over past few weeks.

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SOI is up and down as seen at http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekly

The Australian Bureau of Met have now wound down their El Nino outlook to NEUTRAL for the next few months— They are expecting the current episode to now enter a decay phase. See http://www.bom.gov.au/climate/enso/

 

TROPICAL TOPICS

The recent new moon phase arrived within a few days of the moons perigee and the resulting king tides, combined with some heavy swells, managed to bring sea inundation to Majuro and to some of the northern islands in the Solomons group. The spring tides in January and February get extra oomph from the warm seas in this area and sea inundation seems to be becoming an annual January/February event. See http://www.radionz.co.nz/international/programmes/datelinepacific/audio/20164672/marshalls-braced-for-more-king-tides and http://solomonstarnews.com/news/national/5665-food-shortage-fear

Cyclone NIKO took a brief visit to French Polynesia last Wednesday/Thursday (local dates). The first named system of the year for the South Pacific – Interesting how quickly it blossomed – but it was a small one.

A new MJO cycle is now starting in the Indian Ocean. There are no tropical cyclones around at present but some small depressions in the mid Indian Ocean may deepen later this week.

Extending the MJO cycle seems to have it moving into the Coral Sea area around mid-February.

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MJO time line with blue for the bubbly episodes and yellow/amber for mellow episodes as shown at http://cawcr.gov.au/staff/mwheeler/maproom/OLR_modes/h.6.MJO.S.html

The weekly rain maps over the past fortnight show that the rain associated with NIKO and the South Pacific Convergence zone during last week was the most intense of the planet.

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Weekly rain signatures for past two weeks, as seen at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

WEATHER ZONES

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Weather Zones (see text) as expected mid-week at 0000UTC on Wednesday (GFS/WW3/NOGAPS models) showing isobars, Sig wave height green lines, swell direction arrows SPCZ and STR.

SPCZ=South Pacific Convergence zone.

SPCZ is expected to be strong this week from Tuvalu to Samoa to Northern Cooks with strong westerly winds on its northern side. There is a risk that a low may form on it near Samoa on local Thursday and Friday UTC and then move to Niue area by Sunday UTC /Saturday local.

STR= Sub-tropical Ridge

The STR is well south of normal at present. The large HIGH east of NZ by Monday is expected to only slowly travel east along 45S and should fade near 160W from Thursday.

A replacement High cell should squirt quickly across the south Tasman Sea on Friday and build east of South Island on Saturday, then travel NE to 40S then east along 40S next week.

The next HIGH should cross the central Tasman Sea at a more northern latitude of 35S from Tues 3 Feb

Over NZ/Tasman

The NZ/Tasman area is NORTH of the STR this week, thus dominated by easterly winds.

A weak trough is expected to fade in the north Tasman Sea near 160E with NE winds on its eastern side and SE winds on its western side.

An interesting LOW near 35S 165W tonight is expected to travel westwards towards Northland this week, reaching Northland on Thursday and Friday. This system is caught in some easterly winds aloft, hence its strange track. However the system is expected to weaken away—nevertheless it does have some strong SE winds and 3 metre +  easterly swells on its western side, especially on Tuesday and Wednesday (local).

On Thursday, a LOW is likely to form in mid Tasman Sea, east of Tasmania. This should then cross the South Island on Saturday/Sunday, and bring a front/SW change to North Island on Monday/Tuesday 2/3 Feb, finally bringing some welcome rain.

See my yotpak at boatbooks.co.nz/weather.html for terms used.

Weathergram text only (and translator) is at weathergram.blogspot.co.nz

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