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

25 March 2018

Bob Blog for 25 March 2018

WEATHERGRAM

YOTREPS

 

Compiled Sun 25 March 2018

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.

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TROPICS

Cyclone MARCUS, after hitting Darwin as a CAT 2 system last week, intensified to a CAT 5 cyclone, but is now weakening.

See mashable.com/2018/03/21/cyclone-marcus-strongest-storm-2018/#GOM9uShzdiqQ

 

NORA has moved onshore from the Gulf of Carpentaria onto northern Australia and is now weakening.

 

IRIS formed over Vanuatu is the past few days and is now travelling south across the Coral Sea. It is likely to encounter a jetstream on the northeast side of an upper trough by mid-week. This may well rip IRIS apart, but some models are indicating that the surface part of this system may then travel west or east for a few more days.

 

And a cyclone is now starting to form in Micronesia and is expected to travel north then northeast this week

 

A comparison of the weekly rain map from last week with the previous week shows the path of the cyclones and some heavy rain around Hawaii. Notice that the “equinoctial convergence zone” between south of Galapagos and Marquesas is still there.

 

See trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

 

The SPCZ is at the south-end of its range this week, covering New Caledonia, Fiji and Southern Tonga/Niue.

 

A LOW is expected to form on the SPCZ near 25S to south of Southern Cooks by mid-week, and then to travel off to the southeast.

 

Subtropical ridge (STR)

Large HIGH to east of NZ that dominated proceedings last week is expected to finally shift off to east along 45S.  There is likely to be a squash zone between this HIGH and the Low forming south of Southern Cooks.

New HIGH is expected to form in central Tasman Sea on Monday and Tuesday, then travel across central NZ on Holy Thursday and Good Friday. Then it is likely to fade east of NZ on Holy Saturday.

 

Around Tasman Sea

Low crossing south of Tasmania on Monday is likely to bring a gale to Bass Strait. As a consequence, the start of the Melbourne to Osaka yacht race has been delayed. Associated front is expected to cross South Island on Tuesday, and as a weak front over North island on Wednesday.

Another front is expected to travel onto South Island on Holy Saturday.

 

Panama to Galapagos /Marquesas

Today’s data the weather pattern is looking good for a departure from Panama any day this week.

Between the south of Galapagos and Marquesas there is the “equinoctial” convergence zone, mainly along 5 to 6S between 90W and 115W. Something to avoid.

 

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