WEATHERGRAM
YOTREPS
Compiled Sun 24 December 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.
Merry Christmas to all readers of this blog…
The Tropics:
This current period of increased risk of cyclone formation, due to a passing MJO , has now peaked and should decline next week. It has produced quite a crop of cyclones, mainly in the northern hemisphere. TC KAI-TAK has gone off west of Philippines and is fading away over central SE Asia. TEMBIN is visiting Philippines and has been vicious, with a death toll of more than 180, at this special time of year. Makes me feel their family's sorrow.
The next one for the northern hemisphere is 98W, which is currently located as a weak feature very near the equator, sort of defying the principle that weather features can not rotate at the equator.
In the southern hemisphere we have has a Low TD93P within the South pacific Convergence zone for the past few days, and Fiji Met have been keeping a close eye on it. It now seems to be starting to weaken and is expected to travel Southeast.
That leaves TD 92S, very weak at present in the Timor sea a, and this may deepen as it travels southwest over next few days, and may make landfall over northwest Australia mid-week.
Looking at the weekly rain maps from last week and the week before, at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, we can see pockets of intense convection around SE Asia, Philippines and northeast of Papua New Guinea, corresponding to Kai-Tak, Tembin and TD98W.
WEATHER ZONES
SPCZ=South Pacific Convergence zone.
There are no more near-equatorial westerlies —a sign that this MJO is peaking and will the SPCZ will soon relax.
The SPCZ has split into two zones… an eastern zone of active convection that is being taken off to the southeast by TD93P, and a new zone of building convection over the Coral Sea.
93P is expected to travel SE to south of Fiji, reaching Minerva area on Boxing Day. Avoid.
Subtropical ridge (STR)
HIGH to east of South Island is moving off to the east.
New HIGH is expected to travel east across Tasmania on Tuesday/Boxing day and then onto South Island on Thursday, and then east along 45Souh to east of NZ.
Troughs over NZ:
Trough/cold front is expected to cross South Island on Monday and North island on Tuesday, followed by a South to Southeast wind flow, and deepening into a low east of the North Island on Wednesday, travelling east along 35 to 30S with large SW swells following it. With all these southerly winds from Tuesday afternoon, avoid the Hawkes Bay/Gisborne coast.
Looks Ok for Auckland yachts heading north after Christmas after the front’s peak winds on Boxing Day morning.
Next trough, following the next HIGH, is expected to start moving from Tasman Sea onto South Island on Saturday and further east later. Anticipate a period of strengthening N/NW winds ahead of this system for several days.
Sydney-Hobart
As the Tuesday Tasmanian high travels off to the east, expect an increasing NE flow on its back end, with thermal fluctuations to the wind direction along the coast.
Warm front on Friday and cold front with west/SW change on Saturday.
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