Bob Blog

WEATHERGRAM

YOTREPS

Issued 28 December 2014

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 Ocean: extra heat has been stored in the Pacific Ocean for a while now and all the Oceanic indices have crossed the threshold into El Nino territory.

The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin. It has been negative since July and dived below -10 (Australian units) for much of September, and again for a week in November, then relaxed in early December, but last week started another negative dive. The atmospheric El Nino is stuttering.

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SOI as shown at http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekly showing that there is sufficient heat in the sea to form an El Nino.

In an El Nino event the latitudes of the normal weather zones are drawn closer to the equator, causing the South Pacific Convergence zone to shift further north and east of its normal position.

TROPICAL TOPICS

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

The tropical low that formed last Wednesday between Samoa and Rarotonga/Tahiti has travelled SE and faded. Rain intensified in the South Pacific Convergence Zone last week, as shown in the two rain maps above. It also reached deluging levels over Sri Lanka (with the arrival of a tropical Low) and over Malaysia (as a monsoon) , the most intense in Malaysia in decades.

Also at present there is a tropical depression situated east of Philippines, travelling west, also TC KATE to SW of Cocos Island in the South Indian Ocean. And in the South Pacific another tropical low has formed today, just east of Samoa.

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Fiji Met Service analysis at 3pm local this afternoon as at http://www.met.gov.fj/aifs_prods/0991.jpg

The latest thinking is that this system may soon move SSE with slight intensification getting close to Niue/Rarotonga by local Monday.

Tropical Disturbance Summary For area Equator to 25S, 160E to 120W

ISSUED FROM RSMC NADI Dec 28/0126 UTC 2014 UTC.

TROPICAL DEPRESSION TD05F CENTER [1000HPA] ANALYSED NEAR 13.0S 169.0W

AT 280000UTC. TD05F SLOW MOVING. POSITION POOR BASED ON MTSAT IR/VIS

IMAGERY AND PERIPHERAL OBSERVATIONS. SST AROUND 30 DEGRESS CELCIUS.

CONVECTION REMAINS PERSISTANT IN THE PAST 06 HOURS. ORGANISATION REMAINS POOR. THE SYSTEM LIES UNDER AN UPPER DIFFULENT REGION IN A MODERATE SHEARED ENVIRONMENT. OUTFLOW GOOD TO THE SOUTHEAST. CYCLONIC CIRCULATION EXTENDS UPTO 500HPA.

GLOBAL MODELS HAVE PICKED THE SYSTEM AND MOVE IT SOUTHEASTWARDS WITH SLIGHT INTENSIFICATION.

POTENTION FOR TD05F TO DEVELOP INTO A TROPICAL CYCLONE IN THE NEXT 24 TO 48 HOURS IS LOW.

NO OTHER SIGNIFICANT TROPICAL DISTURBANCE ANALYSED OR FORECAST IN THE AREA.

Fiji Met Service tropical disturbance discussion above is as at http://www.met.gov.fj/aifs_prods/20036.txt

If you are in this area then please remain vigilant and keep up to date with these latest TC bulletins.

WEATHER ZONES

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Weather Zones (see text) as expected mid-week at 0000UTC on Wednesday (GFS/WW3/NOGAPS models) showing isobars, Sig wave height green lines, swell direction arrows SPCZ and STR..

SPCZ=South Pacific Convergence zone.

SPCZ is strong east of the dateline with strong NW winds on its northern side, strong SE winds on its southern side and gale force squalls in-between. A new branch is expected to form over Coral Sea from mid-week.

STR= Sub-tropical Ridge

A new High cell is crossing the South Island tonight and is expected to merge with the quasi-stationary high near 40S 170W by mid-week, making a larger High centered near 45S. This High should then travel east for the remainder of the week along 45S.

The next High is expected to enter the central Tasman Sea on Wed/Thu and fade on Friday. Another High is expected to cross Tasmania on Thursday and then move east crossing central NZ over Sat 3/Sun 4 Jan. Good by then for holiday weekenders.

Over NZ

Trough between Highs is expected to reach central Tasman by Tuesday and cross NZ on Wednesday in time for local New Year’s Eve. This should be followed by a period of disturbed SW/S winds and fronts on Thursday and Friday.

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

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

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