Compiled Sun 30 June 2019
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.
Sea Surface temperature anomalies as at end of April may be seen at www.weatherzone.com.au/climate/indicator_sst.jsp?lt=global&lc=global&c=ssta
The main pattern changes are a return to near normal across the central and south Pacific, but still slightly warmer than normal around NZ and Tasman Sea. Similar easing of warm anomalies are occurring in Indian and South Atlantic Oceans. A zone of cool is now established west of Australia (part of a Positive Indian dipole, depriving Australia of rain from the west). The med is hot. And both the Southern Ocean and the Arctic have lots of cool melt water.
To see how the annual weather cycle and the seasons are working out, we can check the average isobar maps for past 30 days and their anomaly from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html
The subtropical ridge is stronger than normal, especially in the Southern Hemisphere, due mainly to an anomalously intense and slow-moving High (1042) in late June, now east of NZ.
The ITCZ trough has deepened and shifted north especially over Asia. This year’s Indian monsoon was late this year, and, to Jun 26th, its rainfall was 24% below average. It should reach Delhi from 3 July.
Zooming into the NZ area, and comparing monthly anomalies from end of last month with now, shows that the subtropical ridge STR has strengthened, especially over Australia, and its southern parts have drifted south (except over NZ). Troughs are deepening east of NZ, increasing the SW winds.
The latest cyclone activity report is at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html
TC ALVIN briefly bloomed during the week near west of Mexico. TC FOUR is near the Philippines.
There are areas of potential development in the China Sea, near Bangladesh, and to west of Mexico.
SPCZ=South Pacific Convergence zone.
The SPCZ stay over Solomons and another branch stretch from Samoa to Suwarrow to French Polynesia north of normal. There is a trough (1011) lingering around east of New Caledonia for Monday and Tuesday and then that should go south and cross NZ on Wed and Thu.
Subtropical ridge (STR)
Here’s a snapshot of that Big fat High when it was crossing NZ yesterday
This Big fat High is expected to travel east to east of NZ along around 38S and possibly reaches its peak of 1042 hPa on Wed UTC. Long lasting squash zone on its northern side means “stay-out and hunker down” for yachts between French Polynesia and Tonga this week.
Next HIGH is expected to move from Tasmania to Tasman Sea on Friday at 1030+, and then go NE across the Tasman Sea and easing to 1020 near Northern NZ mid-next-week.
Tasman Sea /NZ/Aus
Between the Highs, a trough is expected to move from South Tasman by Tuesday and the merge with a trough from the north over the North Island on Wed/Thu, followed by a southerly flow on Friday/Saturday.
Departures from NZ to tropics should wait until the Southerly arrives, and maybe wait another day for northeast swell to ease.
The trough east of New Caledonia is turning winds between New Caledonia and Australia to a light south-southeasterly for Monday, briefly helping voyages between Noumea and Australia and between Australia and Noumea.
However, by Wednesday to Friday, a squash zone is expected to form SE of Bundaberg due to an incoming High, worth avoiding.
Tahiti to Tonga
Squash zone this week on northside of BFH. Stay put.
If you would like more detail for your voyage, then check metbob.com to see what I offer.
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