Weathergram

WEATHERGRAM

YOTREPS

Issued 20 Jan 2013

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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

The Atmosphere: The Southern Oscillation Index or SOI (30 day running mean) was hugging the plus 0.5 value in Sep Oct Nov, during December it dived to almost minus 1, but in January it has relaxes and is, on the 20th, near plus 0.2.

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Image from Farmonline.com.au showing recent trend in SOI, updated weekly.

The Ocean: Sea surface temperatures across the equatorial Pacific act as a thermostat for the planetary weather engine. When they are different from normal we get a change in clouds around the equator and this changes the earthly wind zones and has an impact on the latitude zones of weather.

Well, in the past month the SST in this target zone has mostly been around normal, and so the oceanic pattern is neither El Nino, nor La Nina; it remains neutral.

WEATHER ZONES

The monsoonal trough over central Australia continues to have little cloud and rain—this is why the Australian continent is acting something like a hot plate left out in the sun and having a continuing heat wave. A few thunderstorms, but their lightning is triggering bushfires. Meanwhile the clouds have been lingering over Indonesia, creating floods. Not normal.

Some cloud and rain is settling over Northern Aussie this week.

The South Pacific Convergence Zone SPCZ currently extends along 10S from Tokelau to Tuvalu and south across the Cook Islands. There is a tropical depression between Rotuma and Futuna … hard to say what its future may be at this stage.

MADDEN JULIAN OSCAILLATION

Madden and Julian were meteorologists who in 1971 published their discovery of a process by which energy for promoting convection and tropical cyclone formation travels from the Indian Ocean to the Pacific Ocean. This is now called the MJO (Madden Julian Oscillation), AND one of these is likely to arrive in the Coral sea this week, making the next few weeks likely to be ‘the business end’ of this tropical cyclone season. Computers are expected tropical cyclones to occur in NW Australia, the Gulf of Carpentaria, the Coral Sea and/or over Samoa heading for the Cooks.

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This image, from www.bom.gov.au shows blue for bubbly and yellow for mellow longitudes across the South Pacific (2.4S to 17.5S) at different longitudes (across the page) over time (down the page). The blue bubbly zone entering the SPCZ this week is an MJO.

At present there is not much happening- except for that TD between Rotuma and Futuna. Basically this is NOT a week to go to sea in the South Pacific, but details are still unsure.

TASMAN SEA/NZ TROUGHS

Large High is crossing central NZ from Mon/Tue 21 to 22 Jan. A weak replacement trough is likely over the South Island on Wed 23 Jan and North Island during the local morning of Thu 24 Jan.

Another High in the Sub Tropical Ridge is expected to move across NZ on Thu /Fri 24/25 Jan and linger to east of NZ until the start of next week.

So, it’s a week of summer sailing over NZ.

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

Weathergram with graphics is https://metbob.wordpress.com

Weathergram text only http://weathergram.blogspot.co.nz

Website http://www.metbob.com

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