Bob Blog

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.

Compiled Sun 24 January 2021

 

So how windy was that storm or how extensive was that calm zone that affected your last voyage?

 

If you are interested in looking at the wind flow that affected any of your voyages in the past three years then I recommend the site manati.star.nesdis.noaa.gov/datasets/SSCATData.php

This shows the latest winds as measured by the Scatterometer satellite (see en.wikipedia.org/wiki/Scatterometer). It defaults to wind vectors at 10x15 (12.5km resolution) and a map for its latest ascending and descending passes over the planet--- and you can click on this map to zoom in to data over an area 10deg lat x 15deg Long . There are gaps of “no data” between passes.

 

Note that this imagery is from the REAL WORLD, but, due to assumptions in the data conversion, isn’t 100% accurate. It is better than the data you see from the NOAA GFS computer model output that you can view on windy.com. Both show, for example, coastal wind acceleration around the North Island East cape, but the scatterometer has a better resolution. Also, the computer model is somewhat inexact with the winds over the South Taranaki bight and a lull west of Taranaki when compared with the real world as seen on the scatterometer.

 

 

One tool that is available on this web site is access to archived data near the top of the page:

The archived data (given in UTC date) goes back to 2019, so you can dial up the imagery and see the details of the winds that affected your last voyage. Plug in the date of your choice and press “Get Images”.

 

The website also offers access to the ASCAT data which dates back to 2007, but this satellite has about 50% of no-data between passes so is less useful.

 

The Tropics

The southern Indian Ocean remains the basin of attention. Cyclone ELOISE made landfall over Mazambique yesterday, and another cyclone (13S) is forming over the ocean. There are some zones of high potential for tropical cyclone formation around north Australia, stretching to New Caledonia and Fiji.

 

The active part of Madden Julian Oscillation (MJO) is expected to travel across the South Pacific over the next few weeks , increasing the potential of tropical cyclone formation.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is spread out from Coral Sea to Vanuatu to Fiji and intensifying. The risk of a tropical cyclone forming during the next week or to is HIGH and a tropical low is expected to form between Vanuatu and Fiji by mid-week.

 

Subtropical ridge (STR)

HIGH 1018 in north Tasman Sea is expected to fade away over northern NZ by Wednesday .

New HIGH is expected to spread east along 45S past the south of Tasmania on Wednesday and reach southern NZ by the weekend.

 

NZ/Tasman troughs

Strong westerly flow over southern NZ on Monday and Tuesday.

Trough is expected to cross NZ on Wednesday followed by a southerly flow on Thursday.

For the start of the Prada Cup semi-finals on Fri-Sat-Sun 29-30-31 Jan, the outlook is for a SW wind on Friday, then NE winds on Sat and Sun.

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

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

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