Issued 05 August 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.
The Ocean: Seas surface temperature anomalies around the Galapagos have been sneaking progressively above normal for the past month indicating that we are on the verge of a new El Nino episode, but we are NOT anywhere near there yet.
The Atmosphere: The Southern Oscillation Index or SOI is now dipping again. Its 30-day running mean rose during July from -1.21 to +0.27 and has dropped to D TO -0.15 by 5th August. So the atmosphere is in neutral territory.
Monsoon is entering the Western North pacific and is currently more active than normal as measured at http://apdrc.soest.hawaii.edu/projects/monsoon/realtime-monidx.html
Tropical cyclones: as the saying goes, August, a must. And indeed it will be a busy week in the North Atlantic with ERNESTO in the Caribbean and FLORENCE in the wins. Meanwhile HAIKUI is hovering near south of Japan and there is another tropical low in mid north pacific waiting in the wings.
Map for GFS model for Wed 8 Aug 1200UTC with features decode given in text.
In the South Pacific, the Convergence Zone SPCZ continues to be fairly quiet. There has been a weak CZ from Solomons to the southeast and this is crossing Fiji tonight, but it is also evaporating because a large area of dry air that has been sent eastwards from out of Australia has caught up with it. Another CZ lies from Tuvalu to Tokelau along 10S, with occasional squalls extending east wards to Marquesas.
This week the CZ near and south of Fiji is expected to blossom into a trough on Wed 8 Aug that is likely to0 then fade over Tonga on Thursday. That’s about all.
SUBTROPICAL RIDGE STR
The STR is in its northern latitude along 25 to 30S and having a weak time this week.
Over Australia the highs are assisted from aloft (probably by extra sinking air thanks to being downstream from the Monsoon) and one should expand on over eastern Oz on Mon/Tue 6/7 Aug and the next should get diverted across Tasmania on Sun 12 Aug.
Further east: One cell is likely to form near 25S 170W on Tuesday 7 Aug and then move East-southeast. Another should form in the same place around Friday and should take a more easterly path High east of NZ near 170W tonight is expected to reform a cell of high pressure between 20 and 30S at 160W on Monday. This new cell should go east and fade away on Tuesday and Wednesday.
We are getting a procession of lows moving across the Pacific, without much opportunity for a high to fit in between them; this is a typical winter pattern, but will probably only last for a few weeks- the pattern started last week.
Last week’s Tasman low is now east of NZ and should get taken southwards across Chathams Islands on Monday. The low which is tonight near south of Tasmania should cross northern NZ on Wed 8 Aug and then rush off the southeast. The trough which is crossing Tasmania on Wed is expected to deepen to around 980 hPa and stall in the Tasman Sea on Thu/Fri/Sat/Sun 9/10/11/12 Aug in the Tasman Sea. Avoid
Traveling towards New Zealand this week:
Only Thursday offers good weather for arrival.
The terms used are more fully explained in the MetService Yacht Pack.
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