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

28 May 2017

Bob Blog 28 May 2017

WEATHERGRAM
YOTREPS
Compiled Sun 28 May 2017

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 tropics
There are two tropical depressions on watch tonight-one in the Bay of Bengal (linked with the arrival of the monsoon) and another in the South China sea.
The status of the tropics as summarized at ruc.noaa.gov/tracks/

There has been a build-up of convection in the equatorial Indian Ocean and this is related to an MJO that is heading east. At this time of year it should induce extra convection around the Philippines in a few weeks.

Rain for the past week is at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif
Trends in the weekly rain maps show that convection remains strong about Indian Ocean to Philippines. Activity is also increasing along the ITCZ.
In the South Pacific there is a clear path of a small low that descended from an upper trough to reach the surface near Fiji and then travel southeast across southern Tonga to Southern cooks. This system gave brief gales to southern Tonga but was NOT a tropical cyclone. See matangitonga.to/2017/05/23/gales-warning-tongatapu

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
Recent activity in the SPCZ was taken away to the SE by last week's low, and all that is left this week is near 5 to 10S, north of its normal position.
Tropical accumulated rainfall for next week can be seen at windyty.com

Subtropical ridge (STR)
High in the Tasman Sea is expected to travel east along 30S this week.
The next High is expected to spend this week over interior of Australia. This means that the nights are now long enough to cool and densify the over continental Australia encouraging the STR to shift north. This High is expected to stretch towards Southern NZ next weekend.

Australia to New Caledonia:
The GO EAST RALLY took the opportunity to sail last week and are now (mostly) in Noumea.
There is a trough crossing Brisbane over next few days so good idea to let that pass and then latch on to the Southerly winds that follow, around Wednesday, for departure.

Departing NZ to the north for the tropics:
The DOWN UNDER RALLY took the opportunity to sail north on Saturday (27th) along with lots of yachts from Opua/Marsden cove. The strong subtropical ridge is likely to ensure a slow trip; however, it should also keep nasty troughs at bay.
A trough is expected to move on to NZ by late Tuesday followed by a Low traveling NE across the country (in upper SW winds) from Thursday to Sunday, followed by strong SE winds.
So those not departing on Monday should wait until AFTER next weekend (Queens Birthday Holiday on Monday) for next good departure opportunity.

New Zealand (Northland) to the east (Tahiti)
Avoid departing on Tuesday because of a likely passing trough.
A Low is expected to take its time crossing the northern NZ region from Thu 1 to Mon 5 June. Any departure from Wed 31 May is likely to encounter too much in the way of easterly winds from that low by Saturday. SO, either go Monday or wait until next week.

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See my website www.metbob.com for more information
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