Bob Blog 18 March 2018

WEATHERGRAM

YOTREPS

Compiled Sun 18 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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A couple of weeks ago I mentioned Jimmy Cornell’s “Ocean Atlas”.

There is also an online site at www.pitufa.at/oceanwinds/  which gives the monthly averaged wins from scatterometer (satellite-derived) wind data.   The data only covers 5-10 years, so is of low quality but is well presented, so you can pan and zoom around the world’s oceans.  Left click on a spot to get a wind rose, and adjust the month at top right to quickly compare one month with another.  This offers a quick way for you to absorb the big picture.

 

EQUINOX

The Latitude of the overhead sun changes throughout the year. The sun is directly over the equator at Tuesday 20 March 1615 UTC (Wednesday morning 5:15am NZDT), and that’s the equinox.  Australia, New Zealand and Samoa switch from Daylight or Summer time to standard time on 1 April.

World Met Day

Another day worth noting this week is World Met day on 23 March. This marks the anniversary of the opening of the World Meteorological Organization as part of the UN in 1950.  This year’s theme is WEATHER READY, CLIMATE SMART, WATER WISE

See  public.wmo.int/en/resources/world-meteorological-day/wmd-2018

TROPICS

HOLA was briefly followed by LINDA in the Coral Sea, but LINDA was blown apart by strong upper winds.

Cyclone MARCUS hit Darwin as a CAT 2 system yesterday.

See www.theguardian.com/australia-news/2018/mar/18/cyclone-marcus-leaves-tens-of-thousands-in-darwin-without-power-or-drinkable-water

It’s been a while since Darwin has had strong winds, so the trees were easily damaged.

Possible future track for MARCUS may be seen at www.tropicaltidbits.com

In the South Indian Ocean ELIAKIM is moving southeast away for Madagascar.

 

A comparison of the weekly rain map from last week with the previous week, as seen at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, shows the path of cyclones HOLA and MARCUS, and a build-up of activity near Micronesia.  There is also a continuation of the “equinoctial convergence zone” between Galapagos and Marquesas.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to remain strong this week and extend all the way across the South Pacific from Solomon Islands to French Polynesia, but with small gaps.

A subtropical low is expected to form near 30S in the trough south of Southern Cooks by mid-week and then travel southeast.  This may become a recurring pattern over the next few weeks, affecting the route between NZ and Tahiti. So, anyone planning this route in next few months should watch how this low behaves.

 

A tropical low is expected to form in the Coral Sea late in the week, and probably travel to the southeast.

 

Subtropical ridge (STR)

Large HIGH east of NZ at start of the week should keep a ridge of settled weather over northern NZ until end of Tuesday. 

New HIGH is expected to travel east across Tasmania from Wednesday and to south of South Island on Friday/Saturday and the northeast to the east of NZ by early next week.

 

Around Tasman Sea

Trough from the SOUTHERN OCEAN is expected to move onto South Island on Tuesday and then stall near central and northern NZ with cold southerly winds from Wednesday to Friday.

 

Panama to Galapagos /Marquesas

Today’s data suggest a departure from Panama before 21 March may be better than  21 March onwards, because the winds near 6N are expected to fade away from 24 March.

Between Galapagos and Marquesas there is the “equinoctial” convergence zone, mainly along 4S between 90W and 105W.

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If you would like more detail for your voyage, then check metbob.com to see what I offer.

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