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

11 March 2012

BOBGRAM issued 11 March 2012

WEATHERGRAM
YOTREPS
Issued 11 Mar 2012
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.

La NINA continues to relax in the atmosphere. Average atmospheric SOI (30day running mean) is now hovering around zero—was 0.3 on 4 March and 0.2 on 11 March

A new pulse of enhanced convection or MJO cycle is still lurking over the eastern Indian Ocean and Northern Australia, but is taking its time getting to Coral Sea—pressure should fall in that area this week. During the past week this pulse has probably been a factor in the formation of TC KOJI and the Low off NW Australia. During the next week it is likely to help form a deepening Low in the Gulf of Carpentaria around Friday 16/Saturday 17 March—this low is expected to travel inland across central Australia next week.

The South Pacific Convergence zone SPCZ had a quiet week in the Coral Sea and seems to be bunched in the Fiji-Samoa-Tonga area and a small low may form on this near or south of Tonga next weekend and then deepen as it wanders off to the southeast.

An interesting phenomenon is occurring near the equator in the near overhead sun (close to equinox) with a zone of convection along around 8 to 10S near Tokelau right across the equator and into the ITCZ near 3N in the eastern Pacific—some sort of mirror image of the ITCZ in the South Pacific, something that I call equinoctial twinning.

SUBTROPICAL RIDGE STR
High1 over central/southern Tasman Sea on Monday 12 March is likely to spread across/around South Island on Tuesday and then wander east steadily along 40/45S.
High2 is, over Mon-wed, being diverted further south across Aussie bight by a low from Australia's monsoonal trough. It should cross South Tasman Sea on Wed and South Island on Thursday, and then wander east along 45 to 40S.
High3 should have a more standard rip across the Aussie Bight and cross just south of Tasmania on Sun 18 March then central NZ on Tues 20 March.

With lowering pressures in the Coral Sea, there are likely to be squash zones of enhanced easterly winds across the South pacific on the north side of these highs.

TASMAN SEA/NZ AREA
Between the highs there are likely to be passing troughs: one is expected to move off to east of North island on Monday, another should reach Southland by Wed and affect east coast on Thursday, a third should reach Southland on Sat and affect rest of NZ and central Tasman Sea on Sunday 18th March.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback: bobmcd@xtra.co.nz, or bobmcdavitt@hotmail.com

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