Weathergram

WEATHERGRAM

YOTREPS

Issued 13 Jan 2013

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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

The Atmosphere: The Southern Oscillation Index or SOI (30 day running mean) was hugging the plus 0.5 value in Sep Oct Nov, and during the last few weeks it dived to almost minus 1, but as at 13 Jan has relaxed again to near zero.

The Ocean: Sea surface temperatures across the equatorial Pacific act as a thermostat for the planetary weather engine. When they are warmer than normal ( El Nino) we get more evaporation and clouds in that region and this augments the earthly wind zones and has an impact on the latitude zones of weather.

image

SST anomaly  map as from http://www.cpc.ncep.noaa.gov/

Well, in the past month the SST in this target zone has mostly been slight below normal, and the oceanic pattern is neither El Nino, nor La Nina, it remains neutral.

Look at this latest available SST map to see that there is a much warmer than around the seas neighboring NW Australia. This is the source area for TC NARELLE which is side-swiping west Australia this week.

WEATHER ZONES

The monsoonal trough is sitting over central Australia as is normal for this time of year, but its clouds and rain are late—may arrive later this month—and so Australian continent has become something like a hot plate, heating up in the sun. This explains its continuing heat wave. The latest pressure and rain map for the region shows this, along with path so far of TC NARELLE and some likely future paths of that system. It also shows the STR Sub tropical ridge from Aussie bight to north of NZ, and the SPCZ South Pacific convergence zone, which is now covering a wide latitude band. The tropical Low near Tonga is expected to deepen over next few days over NIUE and SOUTHERN COOKS and then go off to the south. BRACE FOR IT.

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Google earth using Weather tiles and CIMSS Tropical Cyclone kml addins

TASMAN SEA/NZ TROUGHS

The incoming jetstreams has been crossing the mid Tasman Sea. This has been controlling the fronts crossing NZ— they have been very active over the South Island, but weakening over the North Island.

image

Jetstream from http://squall.sfsu.edu/scripts/shemjetstream_model.html

Surface Low that is now in the mid Tasman is expected to deepen as it crosses central NZ on Tuesday and Wednesday. Avoid any sailing these days. This should be followed by another summer High for another summer weekend.

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