Bob Blog 24 April 2016

WEATHERGRAM

YOTREPS

Issued 24 April 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.

The Tropics:

Cyclone FANTALA is now weakening but developed to produce winds up to 150 knots (173 mph) on Monday, surpassing the 145-knot (167 mph) barrage of GONU (2007). And so FANTALA now holds the record for the strongest Indian Ocean Cyclone on record. Its track did go SE for a while then reverted to NW.

image

Another system that has had a peculiar track is TC AMOS. In my last weathergram it was TD17F bringing heavy rain to Fiji:

(Fiji Met Service threat map, timestamps in UTC)

When TD17F developed into TC AMOS (between Rotuma and Wallis Islands) it was forecast to travel to south coast of Samoa and peak on Saturday night/Sunday morning (local date).

image

Well, AMOS didn’t do as it was ‘told’, and during Saturday changed direction for Samoa’s north coast, and peaked earlier than expected, thus not living up to its full potential. Something like a typical teenager.

image

Map from Samoan Met Service site issued earlier today (Sunday local)

TC AMOS is now turning to the south and well to the southeast of Pago Pago

It brought a brief burst of wind to Pago and, from the wind record we can see that it travelled southeast around the northeastern side of Pago.

image

Barometer dip as AMOS passes by at 23 Apr 1500UTC as seen at www.aviador.es/Weather/Meteogram/NSTU#tabs-2

Wind change from NE to SW observed at Pago, peak gust 47 knots.

image

From http://www.aviador.es

Will TC AMOS be the last cyclone of the season?

Nominally the start of May is the end of the cyclone season. And normally, even though the sea surface temperatures under the South Pacific Convergence Zone are warm enough to trigger cyclones all year round now-a-days, May to October are USUALLY cyclone free, HOWEVER. We had Cyclone RAQUEL last June/July, and tropical depressions can form in any month with squalls that have gale winds, SO it is wise to remain vigilant, anticipate gales in the South pacific during any month of the year, AND get weather updates to help avoid the worst for your voyage.

With WINSTON and then FANTALA both breaking records, there are some saying we have gone past the tipping point and can now expect more extreme storms more often – well that’s just extreme talk, and we are now entering the quieter time of the year, and its getting colder by the week in the non-tropics of the South Pacific, SO let’s take our opportunities and go SAILING into the tropics. That’s what we are here for.

Rain maps for the past fortnight show that the extra convergence zone that has been located between Galapagos and Marquesas is showing signs of weakening. It also shows the heavy rain of AMOS and FANTALA.

image

image

Rain for the past fortnight from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

Panama to Galapagos:

Just headwinds this week. It is possibly too late now to get a good voyage to Marquesas. If anyone is still waiting then let me know.

Travelling to Marquesas:

Now that the convergence zone that was in-between Galapagos and Marquesas is weakening away, the optimal route may be north of the direct route, making use of the strong near equatorial currents. Winds near Isla Isabela are expected to be Ok for departure from local Tuesday, but rather light before then.

WEATHER ZONES

image

Weather Zones (see text) as expected mid-week on Wednesday (GFS model) showing wind, isobars, Sig wave height green lines, SPCZ and STR.

SPCZ=South Pacific Convergence zone.

SPCZ is expected to be weakened this week as TC AMOS takes a lot of energy away.

However there is still plenty of activity around Tuvalu and Southern Cooks/parts of Tahiti.

STR= Sub-tropical Ridge

This week’s Tasman Sea High is further north than last week’s, a sign that we are getting closer to winter. It left New South Wales today and is expected to travel slowly across mid Tasman Sea and weaken over the North Island around Friday. By then, another more southern high is expected to build east of the South Island and then travel northeast across Chatham Islands on Saturday.

There is expected to be a weak squash zone on the north side of this week’s HIGH—north of 30S on Monday and travelling further north and fading over New Caledonia on Wednesday/Thursday.

Between NZ and the tropics

It is a good week of opportunity for going north out of NZ. There may still be some left-over slop in the sea state on Monday, but Tuesday/Wednesday looks great for departure to the tropics. There may just light winds for starters from Thursday until end of the week, and the next passing front in the Tasman Sea is expected to reach from Noumea to Northland by 4 May, so you should attempt to depart before 1 May to avoid its worst—and then again it may be less than strong north of 30S.

After 1 May the next window is likely, at this stage, to be around 10 May. May be better to go this week than next week.

>>>>>> 

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

See my website http://www.metbob.com for information on tailor-made voyage forecasts– Feedback to bob@metbob.com. Tell anyone you like that to subscribe they should email me.

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.

To unsubscribe from WordPress: click the “unsubscribe” link on the bottom of the email. Or, if email wasn’t from WordPress then send a reply email saying LEAVE.

Advertisements