Bob Blog 27 Nov 2016

WEATHERGRAM

YOTREPS

Compiled 27 November 2016

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 Tropics

A tropical low formed in Coral Sea last week and faded as it travelled southward to west of New Caledonia.

We start this week with another tropical low in the Coral Sea, and this one is likely to fade somewhere near New Caledonia mid-week. It has been picked up in the tropical tidbits web site and here is its likely track according to some weather models:

image

As seen at http://www.tropicaltidbits.com/storminfo/96P_tracks_latest.png

Fiji Met service is watching another tropical low tonight located near Rarotonga. Their latest idea on its future can be downloaded from http://www.met.gov.fj/aifs_prods/20036.txt

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

ISSUED FROM RSMC NADI Nov 270833 UTC.

TROPICAL DISTURBANCE 02F [1006HPA] WAS ANALYSED NEAR 20.0S 164.0W AT

270600UTC.

TD02F MOVING SOUTHEAST AT ABOUT 07 KNOTS.POSITION POOR BASED ON

HIMAWARI-8 AND GOES IR IMAGERY WITH ANIMATION AND PERIPHERAL

OBSERVATIONS. SST AROUND 27 DEGREES CELCIUS.

CONVECTION REMAINS PERSISTENT NEAR LLCC. ORGANISATION REMAINS POOR.

CIRCULATIONS EXTENDS UPTO 700HPA. TD02F LIES JUST EAST OF AN UPPER

TROUGH IN A MODERATE SHEARED ENVIRONMENT.

MOST GLOBAL MODELS HAVE PICKED UP THE SYSTEM AND MOVE IT TOWARDS THE

SOUTHEAST WITH SLIGHT INTENSIFICATION.

POTENTIAL FOR TD02F 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.

Rain accumulation maps shows easing activity around French Polynesia, continuing activity in the Coral Sea area and around central America, and an increase in activity over equatorial Indian Ocean. The burst of rain west of Hawaii from a rather peculiar moving tropical depression.

image

image

Rain for the past fortnight from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

WEATHER ZONES

image

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

SPCZ=South Pacific Convergence zone.

The tropical low near Rarotonga is expected to move off to the SSE and deepen near 30S. It is expected to “steal” the winds from the French Polynesia /Southern Cooks area and should leave behind a lingering convergence zone.

Another tropical low is in the northern coral Sea and is expected to go Se and fade around the New Caledonia area around mid-week. Worth watching as this is a system that may need to be avoided.

The SPCZ around Tuvalu and Tokelau may drift southwards this week, and remain intense. There could be convective showers over Samoa and Fiji by end of the week.

image

Tropical accumulated rainfall for next week from windyty.com

Subtropical ridge (STR)

The subtropical ridge are continuing to be well defined and reasonably wide., allowing anticyclones to migrate easterly in a patterned fashion.

The HIGH which is in the western Tasman sea tonight is expected to travel east along 30/33S this week crossing northern NZ on Tuesday /Wednesday.

There may be a squash zone of enhanced westerly winds south of this high, especially until Tuesday, but it seems to be reasonable on north side of this high.

Another High is expected to follow across the South Tasman Sea on Tue and Wed and then stall over central NZ on Thursday and Friday, and move off to east of NZ this weekend.

These subtropical highs offer reasonable weather for any yachts still seeking to get from tropics to NZ/Australia, however there are light winds in the centre of the ridge, and there are troughs in-between the ridges, so travelling in the winds around the back side of a passing ridge may require sailing thru a trough—that’s OK if you do it at a good latitude mid trip, but may be disconcerting if both you and the trough arrive at the destination the same day.

Tasman Sea/NZ Area troughs.

Strong westerlies over NZ on Monday and Tuesday, then the next trough should arrive over the weekend and linger over North Island early next week.

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