Bob Blog

WEATHERGRAM

YOTREPS

Compiled Sun 05 May 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 APRIL

Sea Surface temperature anomalies as at end of April may be seen at www.weatherzone.com.au/climate/indicator_sst.jsp?lt=global&lc=global&c=ssta

The main pattern changes are a slight reduction in the warmth of the Coral and Tasman Sea, a shifting to south of Australia of the cool pool that was in the South Indian Ocean, and the growth of some cool water in the Humboldt current off the west of South America.

It is sad to see these maps are mostly warm, and that the cool areas seem mainly to be melt water around the Arctic or Antarctic.

 

To see how the annual weather cycle and the seasons are working out, check the average isobar maps for past 30 days and their anomaly from www.esrl.noaa.gov/psd/map/images/fnl/slp_30.fnl.html

The subtropical ridge has had a strong month around the Sothern hemisphere, and has been split into three in the northern hemisphere. The lower than normal pressures to south of Australia are interesting.

Zooming into the NZ area, and comparing monthly anomalies for end of March with end of April, shows that the main difference is the building of High pressure over Australia, and a slight weakening of high pressure east of NZ. This means there has been a switch over NZ from mostly NE winds to mostly SW winds.

 

The last 30 days of rainfall, and its anomaly are seen at trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.html

This web site seems to be having problems at present and latest data is 23 April.

Some tropical cyclone tracks in the Indian Ocean stand out. The ITCZ has been wetter than normal across Micronesia, and below normal near Galapagos. There is a “mirror Convergence Zone” along 5degrees south in the Eastern Pacific. There are dry patches appearing in the South Pacific.

 

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THE TROPICS

TC FANI has finally weakened after devasting parts of the NE coast of India.

The active phase of MJO is travelling into the western pacific this week.

There are no tropical cyclones around tonight, but there are potential areas for development mainly around north Coral sea and Micronesia. The GFS model currently is running away with the idea of a Tropical cyclone forming in the Coral sea by mid-week and maybe developing and curving counter-clockwise around New Caledonia this weekend. The EC model has a low, but it is weaker and later. Each new GFS run over the past few days has been delaying things, and that is a sign that it doesn’t have a good grasp. The models disagree a lot at this stage, and there is uncertainty until their scenarios get closer.

TC in the tropics at present, with latest cyclone activity may be seen at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is expected to intensify in the Coral sea this week, and spread south. The models agree that a tropical Low forms by around mid-week, but disagree as to if/when it deepens and how fast it travels south. Should be a branch of SPCZ from Samoa to Southern Cooks.

 

Subtropical ridge (STR)

HIGH over 1030hPa traveling around south of South Island tonight is expected to then go NE along 45 to 40S east of NZ. This high should block the troughs in the Tasman Sea until this weekend.

 

Tasman Sea troughs

Low is travelling south into the South Tasman sea on Monday and fading by Wednesday.

Next Low is expected across Bass Strait by Thursday and then across NZ by Sunday 12 May=Mother’s Day.

 

Australia to New Caledonia.

If the GFS model is correct, then a low from the tropics may curve around New Caledonia 11/12 May. That’s no good. Stay put and hope for something better next week.

 

NZ to Fiji/Tonga

With such a dominant High to east of NZ there is a possible departure on Monday, but after that there is too much NE wind between NZ and the tropics until that trough crosses NZ on Mother’s Day. There maybe a good enough departure next week, but unsure at this stage.

 

Panama to Marquesas

Light variable winds in the Gulf of Panama for a motoring start. Then mainly SW winds between 5N and Galapagos area so some tacking may be required for that. Trade winds from the SE are likely for west of around 100W so that’s when to turn to Marquesas.

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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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