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

13 March 2016

Bob Blog 13 March 2016

WEATHERGRAM

YOTREPS

Issued 13 March 2016

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.

Next edition is likely to be postponed to Monday 21 March  I’m off to WOMAD  next weekend: http://metbob.us12.list-manage2.com/track/click?u=297f1d13c59cf6261733851cb&id=25ad564e0e&e=78b77fda36

 

How is El Nino doing?

The Southern Oscillation index is still well in the “pink”= El Nino range.

SOI may be seen at http://metbob.us12.list-manage.com/track/click?u=297f1d13c59cf6261733851cb&id=8ef5bedf6d&e=78b77fda36

 

The amount of heat stored in the target area is slowing easing now.  This event is lasting longer and got slightly stronger than the 1997/8 event (as measured looking at the NINO3.4 index) at

http://metbob.us12.list-manage.com/track/click?u=297f1d13c59cf6261733851cb&id=9ae65c7b2a&e=78b77fda36

Those of you travelling to Marquesas may have heard rumours of weaker than normal trade winds ---well over the past month, the data shows that along the equator the trade winds have actually been slightly STRONGER than normal. That’s good for you.  However the data also shows there have been a few “puddles of calm” near the Central American coast.  These can be a problem.

Wind averages and anomaly for past month may be seen at

http://metbob.us12.list-manage1.com/track/click?u=297f1d13c59cf6261733851cb&id=5df4120ac8&e=78b77fda36

This map also shows that there are really only three features that show up in the monthly average—(even WINSTON didn’t make much of a monthly mark) there’s an anomalous HIGH to NE of NZ, another in the North Atlantic, and a large anomalous LOW over the Aleutians.  These features may last long enough to impact on weather for the next fortnight.

The TOA data for yesterday does show a slight westerly anomaly along the equator—but only from 180 to 140W and not enough to cancel out the trade winds.

See http://metbob.us12.list-manage.com/track/click?u=297f1d13c59cf6261733851cb&id=e9ffbada6e&e=78b77fda36

 

The Tropics:

No tropical cyclone anywhere for now.  However there may be something brewing near North Australia in the Gulf of Carpentaria, and this feature may be able to jump into the Coral Sea by next weekend, and grow.

 

Last week I mentioned how the directly overhead sun tends to trigger an “extra convergence zone” that mirrors the ITCZ in the Pacific around the March Equinox.  This zone stands out clearly in the rain map for the past week.  It should weaken towards the end of the month (Overhead sun is to reach the equator on Sun 20 March UTC, a little earlier this year as a consequence of that leap day. BTW, next full moon, the Passover moon is on 23 March UTC, so Easter Sunday follows on 27March).

 

Rain for the past week can be seen at  http://metbob.us12.list-manage.com/track/click?u=297f1d13c59cf6261733851cb&id=d9af935609&e=78b77fda36

 

Panama to Galapagos:

There is an OK N/NE flow as far as 6N (weak at night) then a zone of light variable winds between 6 and 3N then light tail winds to Galapagos with a reasonable tail current. Convection is mainly at 5N and mostly west of 85W so not much of a problem.  No real advantage this week in going via Isla Del Malpelo, so may as well follow the current to 5deg 30min N 81W then go direct. This waypoint may vary, so email me if you’d like a tailored waypoint.

 

Travelling to Marquesas:

Light tail winds around Galapagos. Very strong tail current along the equator, but the obstacle this week is that extra equinoctial convergence zone.  To avoid it go to 6 or 7S and then go direct.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is expected to spend this week regenerating in the Coral Sea.  We should watch this area for if a low forms there early next week then then it may be on track to affect NZ Easter weather.

That “extra” CZ near 5S is expected to linger this week.  A week trough is crossing New Caledonia early this week and its rain is likely to be south of Fiji by mid-week and over Minerva by next of the week ,  moving east  thanks to upper westerly winds.

 

STR= Sub-tropical Ridge

High east of NZ at beginning of week is fading away.

New HIGH is expected to travel east across southern Tasman Sea on Monday and Tuesday around southern NZ on Wednesday and then to east of NZ along 45S for the remainder of the week.  There is expected to be a squash zone of enhanced easterly winds on the north side of this feature.

 

For NZ and Tasman Sea

Weak front on Monday/Tuesday/Wednesday between the outgoing high and the incoming High.  This front is expected to linger on as drizzly cloud stuck in the eastern Tasman Sea.   Next front is expected to make its way from South Tasman Sea on to Southern NZ this weekend 19/20 March, but may be kept off northern NZ until early next week by the back ridge of the High then east of NZ.  This scenario is likely to bring strong E/NE winds to northern NZ on 19/20 March.

>>>>>> 

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website www.metbob.com for information on tailor-made voyage forecasts– Feedback to bob@metbob.com.

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom right to subscribe.

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