Bob Blog

WEATHERGRAM

YOTREPS

Issued 29 November 2015

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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Tropical Cyclones

That tropical depression we were following last week has deepened into a Category 1 tropical cyclone TUNI. Tropical cyclone TUNI is tonight moving toward the Niue area:

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From Fiji Meteorological service at http://www.met.gov.fj/aifs_prods/65648.html

Last week we also had Tropical Cyclone SANDRA making landfall on Baja California soon after Thanksgiving/Black Friday. –mainly as left over rain.

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The origin of this cyclone was a Tehuantepecer (wind burst funneled by mountains)

(see https://en.wikipedia.org/wiki/Tehuantepecer) earlier in the week.

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See https://youtu.be/TvDT6gsTo8A for a windyty.com animated view of this metamorphic event.

The Weekly rain maps show rain concentrations in TUNI and SANDRA during the past week.

Weekly rain signatures for past two weeks, as seen at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

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WEATHER ZONES

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

SPCZ=South Pacific Convergence zone.

The main part of the SPCZ is strong in activity and extends from Tuvalu to TUNI (between Samoa and Niue) and has squally NW winds on its northern side. There is another branch along 15S across the Cooks and French Polynesia with N/NW winds on its northern side and SE winds on its southern side.

A low centre is expected to form on Monday UTC/Sunday local, near 15S 153W, close to the north side of Maupiti/Mopelia (Maupihaa) and this compact feature MAY develop into a cyclone over Tahiti area by mid-week. The models are forecasting large swells around this feature. Brace accordingly.

STR= Sub-tropical Ridge

The STR is very strong this week with well-marked and slow-moving HIGHS.

A HIGH is crossing central NZ this evening and should travel slowly along 45 to 40S this week, further south than normal.

Another HIGH is expected to envelop the Aussie Bight mid-week and then move into the Tasman Sea on Friday.

Over NZ/Tasman:

Trough preceded by NW winds and with a southerly change reaching Sydney around local Wednesday morning and then Northland by late Friday, then fading away.

Travelling Tahiti to Marquesas.

Convergence zone between Tahiti and Marquesas is too squally, and there is this tropical depression/possible cyclone forming on local Sunday. Best to stay put and tune in to local warnings and brace for strong winds/swell this week.

Between Tropics and NZ:

The lingering High makes travelling from New Caledonia to NZ OK, and should be OK when the wind/swells of TUNI ease around Fiji/Tonga.

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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.

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