Bob Blog 1 Dec

WEATHERGRAM

YOTREPS

Compiled Sun 01 Dec 2019

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.

REVIEW OF THE LAST MONTH

Sea Surface temperature anomalies as at start of November compared with the end of November may be seen at www.weatherzone.com.u/climate/indicator_sst.jsp?lt=global&lc=global&c=ssta

Early November (below)

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Late November (above)

The anomolies in the North Pacific are unchanged. There continues to be a build-up in heat in the Tasman Sea. And sea-temperatures around Galapagos are on the warm (El Nino) side of normal.

To see how the annual weather cycle and the seasons are working out, we can check the average isobar maps for past 30 days and their anomaly from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

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Average for November 2019 (above)

The subtropical ridge in the southern hemisphere has expanded southwards. The area below 1010hPa in the equatorial area has also expanded southwards.

Anomalies October 2019 (below)

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Anomalies November 2019 (above)

Higher than normal air pressure over arctic and Antarctic are helping send cold air equator-wards into the mid-latitudes. There are four low-pressure anomolies around the Southern hemisphere mid-latitudes. Siberian High has formed stronger than normal.

Zooming into the NZ area, and comparing monthly anomalies from last month with now,(but with a change of colouring), shows that the subtropical ridge STR has strengthened and expanded southwards, but the 1010 isobar is still over central NZ .

It remains most intense over SW of Australia, most intense spot has shifted from eastern Australia to west of Australia. Isobars over NZ have weakened, with the 1010hPa isobar in much the same place as last month, and 1005 hPa now further south. Now a NW anomalis flow over NZ

OCTOBER below

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November above

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The Tropics

The latest cyclone activity report is at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at http://www.ssd.noaa.gov/PS/TROP/TCFP/index.html (but not this weekend)

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Active cyclones at present is KAMMURI aiming for northern Philippines.

WATHER ZONES

Weather Zones (see text) as expected Wednesday 00UTC showing isobars, winds, waves(magenta) STR, and SPCZ. Pink area = lightning likely (high CAPE)

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SPCZ=South Pacific Convergence zone.

Tropical cyclone RITA briefly reached Cat 1 (the lowest) just east of northern Vanuatu last week, so our cyclone season has started.

The SPCZ is expected to have a normal week, mainly stretching from Solomons, across northern Vanuatu to between Fiji and Samoa to Southern Cooks.

There is expected to be a passing trough further east.

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Accumulated rainfall for next week from windyty.com (isobars are for Sunday night).

Subtropical ridge (STR)

HIGH east of NZ over 1025hPa is expected to linger near 35S 160W this week. maintaining a disturbed NW flow over the North Island.

Next High is expected to enter the Tasman Sea (from East Aus) over the coming weekend 7-8 Dec.

Tasman Sea /NZ/Aus

Deep lows, one dropping to maybe 951 by Tuesday local, way south in the Southern Ocean, is expected to maintain a series of fronts on the Tasman Sea /NZ area. The quasi-stationary HIGH east of NZ should keep a lot of the rain away from NE of NZ.

One of those fronts may turn into a low in mid-Tasman that may visit NW NZ by Sunday 8 Dec local, 1002 hpa, followed by SW winds early next week, avoid arriving then.

For Noumea to Aus: Mixed bag this week, Northerly winds until Wednesday, then light wind then southeast winds from Sunday 8 Dec. OK to go, but may need waypoints,

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

Contact is bob@metbob.com or txt 6427 7762212

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