Issued 23 November 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 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, slightly relaxed for a while in October, and dived below -10 early in November, but is now relaxing a little .
SOI as shown at http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi, showing that we are now having an at-least-weak El Nino.
Tropical cyclone activity has now reduced to one possible area in the Indian Ocean, and an “area of interest” to the NW of Samoa.
The “area of interest” looks like this on Google Earth at present:
The latest tropical disturbance summary at http://www.usno.navy.mil/NOOC/nmfc-ph/RSS/jtwc/ab/abpwweb.txt has this to say about this system:
ABPW10 PGTW 230600
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/SIGNIFICANT TROPICAL WEATHER ADVISORY FOR THE WESTERN AND
/SOUTH PACIFIC OCEANS/230600Z-240600ZNOV2014//
1. WESTERN NORTH PACIFIC AREA (180 TO MALAY PENINSULA):
A. TROPICAL CYCLONE SUMMARY: NONE.
B. TROPICAL DISTURBANCE SUMMARY: NONE.
2. SOUTH PACIFIC AREA (WEST COAST OF SOUTH AMERICA TO 135 EAST):
A. TROPICAL CYCLONE SUMMARY: NONE.
B. TROPICAL DISTURBANCE SUMMARY:
(1) THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 8.2S
177.1W, IS NOW LOCATED NEAR 11.5S 174.4W, APPROXIMATELY 204 NM NORTH
OF PAGO PAGO, AMERICAN SAMOA. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS UNORGANIZED FLARING CONVECTION ASSOCIATED WITH AN
ELOGATED LOW-LEVEL CIRCULATION CENTER. A 230354Z NOAA-19 MICROWAVE
IMAGE REVEALS VERY FRAGMENTED CONVECTIVE BANDING ON THE EASTERN SIDE
BROADLY WRAPPING INTO THE CENTER. ALSO, A CIMMS 230300Z 850MB
RELATIVE VORTICITY PRODUCT SHOWS AN ELONGATED VORTICITY SIGNATURE.
UPPER-LEVEL ANALYSIS INDICATES THE DISTURBANCE IS LOCATED NORTH OF
THE RIDGE AXIS IN A FAVORABLE ENVIRONMENT WITH LOW TO MODERATE (05
TO 15 KNOT) VERTICAL WIND SHEAR AND EXCELLENT POLEWARD OUTFLOW.
ADDITIONALLY, SEA SURFACE TEMPERATURES WITH A RANGE OF 26 TO 28
DEGRESS CELCIUS IN THE AREA ARE FAVORABLE FOR DEVELOPMENT. MAXIMUM
SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO 25 KNOTS. MINIMUM SEA
LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1004 MB. THE POTENTIAL FOR
THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24
HOURS REMAINS LOW.
(2) NO OTHER SUSPECT AREAS.//
It is judged as having a low chance of any further deepening. The GFS models and their GRIB files are picking that this system may deepen into a depression on Mon/Tuesday and bring clockwise gale winds between the Niuas and Niue, then Southern Cooks on Wednesday/Thursday- but the more reliable ECMWF model suggests this isn’t likely.
Weekly rain maps over the past fortnight show an increase in convection over the past week in the Indian Ocean.
Weekly rain signatures for past two weeks, as seen at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif
This increase in convection in the Indian Ocean is possibly part of a MJO cycle that will gradually make its way into the Pacific Ocean over the next few weeks. For the next week or so it increases the risk of a tropical cyclone formation in the area to NW of Aussie.
For the following weeks this increased risk spreads east
This is shown at http://www.meteo.nc/cyclone/coin-des-experts
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 has strengthened in the past week and is expected to drift south onto northern Tonga and SE onto Niue, then later onto southern cooks. The GFS model is picking that a depression may form on the SPCZ and move along it to the SE, but other models only have a weak feature. The GFS model also has a tropical low forming SE of French Polynesia. These may not actually happen but if you are sailing in these areas this week then brace for strong winds anyway.
STR= Sub-tropical Ridge
The STR is strong and well defined and mostly at its normal latitude for the time of year, but north of normal in the Tasman Sea/ NZ area.
HIGH at 30S between New Caledonia and New Zealand is expected to stay put until Wednesday and then slowly fade away as it travels east from Thursday to Saturday.
NEXT High cell is expected to travel east along 45S from Saturday 29 Nov , reaching North island around Wed 3 December – followed by a northerly flow -that is GOOD for arriving in NZ – late next week (Thursday to Saturday 4-6 Dec).
Between the tropics and NZ
At north Minerva:
Trade winds until Thursday, light and variable on Fri 28 to Mon 1 Dec, then more trade winds. Good idea to depart around Thursday so as to catch a northerly flow when approaching NZ – voyage will encounter a period of southerly winds around Sun 30 Nov/Mon 1 Dec and requires waypoints.
Over northern NZ:
Westerly flow on Monday/Tuesday, then an active trough on Wednesday followed by a SW/S flow on Thursday 27 to Tues 2 Dec. NOT the best week (after Tuesday) for arriving in NZ.
See my yotpak at boatbooks.co.nz/weather.html for terms used.
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