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Bob McDavitt's ideas for sailing weather around the South pacific

16 September 2018

Bob Blog

WEATHERGRAM

YOTREPS

Compiled Sun 16 Sep 2018

 

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.

 

Equinox is next Sunday:

Next Sunday, 23 Oct at 01:54 UTC marks the vernal equinox. At this point in time the overhead sun is directly over the equator, shifting from the northern hemisphere to the southern hemisphere.

 

If you check sunrise /sunset times for your place for Sun 23 Sep, you will find that these compute to something like 12hr 7mins of sunlight. This is because sunrise and sunset are defined with respect to the top limb of the sun, rather than the centre of the sun, and that adds a few minutes of sunlight to the day. You’ll find (if you look) that the day that has closest to exactly 12 hours of daylight, called the equilux, is around three days earlier than the September equinox.

 

Somehow, I was thinking that New Zealand switched to Daylight time on the fourth Sunday of September--- but no, the change occurs on the last Sunday of September, and so that’s 30 September

 

The change to daylight saving occurs on different dates for the nations around the South Pacific so I think it’s a good idea for you to have a summary for reference

 

Date Place Daylight saving time zone

30 Sep New Zealand UTC+13 (NZDT)

30 Sep Chatham Islands UTC+13h45mins (CHADT)

7 Oct Lord Howe Is. UTC+11 (AEDT)

7 Oct New South Wales, Tasmania UTC+11 (AEDT)

4 Nov Fiji UTC+13 (Fiji Summer Time FJST)

No changes in Tonga or Norfolk Island or Queensland or New Caledonia.

 

As yachts start their end-of-spring migration, with the approaching South Pacific Cyclone Season, it is also useful to have a summary of the various national holidays, as these limit available departure dates.

French Polynesia 1 Nov All Saints Day, 11 Nov Armistice day (100th year).

Cook Islands: 26 Oct Gospel day

Niue: Oct 19 to 22 Constitution day celebrations, Oct 22 is also Gospel day.

Tonga Sep 17 HRH Crown Prince Birthday, Nov 5 Constitution Day

Fiji Oct 10 Fiji Day, Nov 7 Diwali, Nov 20 Muhammad Birthday

New Caledonia Sep 24 National Day, 1 Nov All Saints Day, 11 Nov Armistice Day (100th year).

New Zealand Oct 22 Labour day.

Australia: OCT 1 Labour Day (ACT, NSW &SA), Queen’s Birthday (QLD)

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TROPICS

MANGKHUT travelled over the northern parts of the Philippines, with a death toll of at least 24 so far. It is now skirting around Hong Kong. FLORENCE weakened as it made landfall over Northern Carolina and has a death toll of 13 so far.

It is purely a coincidence that the Atlantic systems all have female names at present: The males: Gordon and Isaac have faded away

Also the Southern Hemisphere cyclone season is showing signs of a possible early start with the formation of Tropical depression ONE in the South Indian Ocean.

Map of current storms is seen at tropic.ssec.wisc.edu/

Looks like HELENE may end up over the UK this week.

Looking at the weekly rain maps we can see the tracks of last weeks’ cyclones.

There has been an intense area of rain last week over New Britain to northeast of Papua New Guinea.

See trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stay in the region from PNG to just south of the Solomons Islands to north of Fiji this week.

Trough over Vanuatu on Monday UTC travelling to south of Fiji on Tuesday UTC and fading over south-of-Tonga on Wednesday UTC.

Convergence zone over Tahiti on Tues UTC and Tuamotu Islands to Gambier Islands on Wednesday UTC. Then a Low may form south of Tahiti by end of the week travelling off to the SE and deepening, stealing the wind for Tahiti

 

Subtropical ridge (STR)

HIGH over 1030hPa to eats of NZ travelling east along 40S. Squash zone of enhanced winds on its northern side between 20 and 25S reaching peak on Tuesday UTC.

Next HIGH should move from Australian mainland into Tasman Sea on Mon/Tuesday UTC, and then fade over central NZ.

 

Around Tasman Sea, NZ.

Low1 crossing the South Island on Monday UTC Low2 is expected to be crossing the area between Fiji and NZ on Monday/Tuesday 17/18 Sep, followed by Low3 on Fri/sat 21/22 Sep. Southerly winds follow these lows.

For those sailing towards New Zealand from Fiji/Tonga/Noumea, there may be a narrow gap between these lows, so that the best-looking voyage this week maybe with a TUESDAY departure, but this does involve zig-zagging around some southerly headwinds.

Traffic going from New Caledonia to Australia have useful south to southeast winds for starters but may encounter a front and southerly winds near Australia from Thursday UTC.

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If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

 

09 September 2018

Bob Blog 9 Sep

WEATHERGRAM

YOTREPS

Compiled Sun 09 Sep 2018

 

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 “Olde Man” Southerly

When a low crosses the North Island and the deepens as it moves away, the resulting southerly gale thru Cook Strait lasts for around three days. Such an occurrence is nicknamed by many Wellingtonians as an “Olde Man Southerly”. Its steadiness feels belligerent, lingering longer than desired. At this time of the year the arriving air hovers just below 10 C, but when the wind chill is taken into account is feels less than 4C—colder than the inside of a fridge. This wind has been described as “blowing straight through you” for you feels it’s cold in your bones .

 

We had an Olde Man last week and I was in Wellington to experience it. The weather map (Noon Wednesday local, courtesy of MetService) shows the low responsible.

 

Because this low is close to Auckland, I have heard some smart people claiming that the reason Wellington gets such cold southerly outbreaks can be summed up in two words: “Auckland  sucks”. The map illustrates a classic “eggbeater” with a clockwise spinning wind around the low to the east of the North Island, and a counter-clockwise spinning wind around the High to east of the South Island.

Of course another contributing factor to this Cook Strait gale is the layout of the land, with mountain chains over the South Island and the North Island, Cook strait is the right sized gap to make a “river of wind”.

 

This can be seen on windy.com and also by clicking on Wellington airport a graph of recent data may be seen showing temperature, wind and pressure profile during this “Olde man”

 

This river of wind crosses the isobars toward s low pressure.

1) The switch from Northerly to Southerly is relatively quick, with no real “calm” in between. Also the barometer starts rising hours before the northerly winds fade. image

2) It takes around 12 hours for a SW wind to swing to a southerly and rise to a gale, along with a period of rapid rising pressure.

3) AFTER the Southerly gale starts , the pressure continues to rise, not so fast, but a steady rise from 1015 to 1025hPa over 2 days.

4) Once the pressure peaks and steadies, the wind relaxes just a little. It continues to stay strong for another day or more.

5) Temperature remains much the same throughout the event with no day/night signal. Showers continue until the air dries out and dewpoint drops to below 5C.

 

TROPICS

It is now “busy time” for the Atlantic Ocean. FLORENCE is likely to make landfall in North Carolina, and OLIVIA may visit Hawaii but is expected to weaken in the process. MANGKHUT is heading to the northern Philippines /Southern Taiwan area.

The weekly rain maps show the tracks of last weeks’ cyclones with JEBI across Japan and NORMAN just missing Hawaii. Note hoe the rain associated with the low east of NZ just touched the east coast of the North Island. See www.facebook.com/MetService/videos/891981477639175/

There has been very intense rain associated with a low just south of Tahiti – I’m not sure why this low was so wet.

See: trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stay in the region from PNG to just south of the Solomons Islands to north of Fiji this week.

Low to south of Tahiti is expected to go south and fade next few days.

Passing trough to south of Fiji on Monday UTC and then over southern Tonga on Tuesday UTC and Southern Cooks on Thursday UTC, consisting of erratic winds and possibly a few showers.

 

Subtropical ridge (STR)

HIGH less than 1020hpa is expected to form near 25S South of Tonga on Monday UTC and travel east along 20 to 25S to be south of French Polynesia by Wednesday UTC.

HIGH over 1025hPa over New South Wales on Monday UTC spreading east along 30 to 35S reaching NZ around Thursday UTC and then spreading further east along 35S. There may be a zone of enhanced SE wind so the north side of this High, mainly near 20S.

 

Around Tasman Sea, NZ.

Low is expected to cross northern NZ on Monday and southerly winds following this feature are likely to affect area between NZ and 20S on Tuesday --upsetting sailing between topics and NZ, but OK going t’other way. After that, with high pressures over NZ and trade winds to north of NZ, some good-looking sailing voyages from the tropics to NZ are likely.

Mainly easterly winds in North Tasman sea, so OK to sail New Caledonia to Australia, but not the other way. Traffic going from Australia to NZ may need to get to at least 35S to find a way eastward.

 

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

 

02 September 2018

Bob Blog 2 Aep 2018

WEATHERGRAM

YOTREPS

Compiled Sun 02 Sep 2018

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 AUGUST  2018

Sea Surface temperature anomalies as at end of August  may be seen at www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html

The eastern equatorial Pacific around Galapagos is the focal region for ENSO and is now on a steady warming trend. Temperatures around Australia to New Zealand are becoming below normal, a possible indicator of drier than normal conditions in the next month or so.

The Gulf Stream off the east coast of North America and the Kuroshio current off Japan still stand out as warmer than normal.  These may help steer tropical features away to the northeast.

Warm anomalies continue off west side of Mexico to Hawaii indicating a busy cyclone season for next few months.

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To see how the annual weather cycle and the seasons are working out, check the average isobar maps from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

Average isobars for past 30 days and their anomaly:

The isobar maps show that subtropical ridge in the southern hemisphere is looking robust, as are the North Atlantic and Northeast Pacific HIGHS. The August lows in the Southern Ocean have been favouring three positions: Tasman Sea, SW of South America, and SE of South America.

Lower than normal pressures between Europe and Philippines show a more active monsoon. 

Zooming into the NZ area, the 1010hP (between dark and light blue) isobar has shifted from Christchurch to Gisborne.  And the 1015 has retreated off Tonga.  This explains the increase in westerly winds onto western NZ, and can be taken as an early start to SPRING weather patterns. Not much change around Australia .

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

The rain map shows extra convergence in the ITCZ from Bangladesh to Philippines , and across  the North Pacific Ocean, but it has been drier than normal over the Caribbean..

In the Southern Hemisphere a large dry region stretches from Australia to Vanuatu/Fiji.. It seems that the SPCZ has shifted northwards and estwards (an El Nino trait).

In summary, it seems that, although the atmospheric and oceanic parameters are “neutral” at present, as seen in my last week’s blog, there are also some signs of an El NINO weather pattern.

 

TROPICS

We have reached the time of the year when cyclones cluster, as is happening this week in the northeast Pacific Ocean. 

 For Map of current storms see tropic.ssec.wisc.edu/

There is MIRIAM, NORMAN , and OLIVIA in NE Pacific, FLORENCE in north Atlantic, and JEBI in NW Pacific.

NORMAN is expected to sideswipe Hawaii later this week.

And JEBI is expected to visit Japan this week

 

Looking at the weekly rain maps we can see that the Asian monsoon is active over south China and the Philippines/Indonesia area, and the ITCZ is active across the northeast  Pacific and around Panama. South Pacific Convergence zone is weak and further east than normal.

 See: trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stretch from PNG to the Tuvalu/Tokelau area this week.

Passing trough over southern Vanuatu on Monday and Tuesday is expected to extend SE on Wednesday into a trough southwest of Fiji, the on Thursday turn into a low south of Fiji that then should go SSE to east of NZ.

Trough is expected to form over Tahiti area by local Tuesday, the convergence zone associated with this feature is expected to visit Tuamotu Archipelago to Gambier group around local Wednesday. 

 

Subtropical ridge (STR)

Large High 1035+ at 35S to south of Tahiti should fade and travel east by end of the week.  The squash zone of enhanced easterly winds between it and the Low over Tahiti should peak around mid-week with strong wind and large swells affecting Southern Cooks.  Avoid.

HIGH travelling east across Tasmania on Monday should skirt around south end of NZ on Tuesday and then travel east along 45S to east of NZ on Wednesday.  Squash zone between this high and Lows to east of the North Island should bring a classic “olde man southerly” to central NZ from Monday night until Thursday.

 

Around Tasman Sea, NZ.

High pressures in central Tasman sea this week should ensure good voyages from New Caledonia to Queensland. Traffic going from Australia to NZ may need to get to at least 37S to find a way eastward.

Low is expected to be crossing North island don Monday followed by three days of strong SE winds.  Conditions should be OK again around Friday or Saturday for departing Northland, As for sailing to NZ from tropics, nope, too much southerly this week.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 

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