Bobgram

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.
Compiled Sun 31 January 2021
TC ANA is expected to have peaked as Category 2 over Suva local noon Sunday
and then weaken and travel southwards across Kadavu area tonight and then
off to southeast on Monday.
See Fiji Met Service official track map as at http://www.met.gov.fj/
If you only have access to email then you can download the latest by sending
an email to mailto:query@saildocs.com , no subject needed, with the message:

SEND https://www.met.gov.fj/aifs_prods/20032.txt
Note that the gale winds are in a ring around the centre, Observations of 33
knots (peak 46 knots) at Rakiraki and 38 knots at Undu point at local noon
as seen on windy.com

And the scatterometer (taken when ANA was over Yasawa Islands) shows how the
squall bands spiral not the low centre (see
manati.star.nesdis.noaa.gov/datasets/SSCATData.php) Black data has been
affected by rain.

TC ANA is part of a broad band of lows that stretches all the way across
northern Australia into the Indian Ocean. This monsoonal trough has a zone
of near equatorial westerly winds on its northern side and is a classical
tropical feature brought about as a burst of energy extends eastwards thanks
to a positive phase of the MJO (Madden Julian Oscillation). It will dominate
the South Pacific for next few weeks and is likely to trigger a few more
cyclones, some affecting Fiji.

Monsoonal trough is seen at satview.bom.gov.au/
The Tropics
The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical
Cyclone Potential is from http://www.ssd.noaa.gov/PS/TROP/TCFP/index.html
TC ANA is travelling south over Fiji. There is a Tropical depression
northeast of Espirito Santo which may visit Fiji on Monday, and a tropical
low in the Coral Sea which may visit Vanuatu by Tuesday and New Caledonia on
Wednesday. These systems my briefly become cyclones. And there is a high
potential of tropical cyclone formation along a monsoonal trough from
northern Australia to Fiji. However they are all "feeding from the same
pool" and this means that none of them are likely to reach the higher
categories of wind speed or area coverage. It does mean that heavy rain may
be encountered in many places along the monsoonal trough.


WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is intense from Coral Sea to Vanuatu to Fiji. As part of a monsoonal
trough.

Subtropical ridge (STR)
HIGH 1024hPa over central NZ is slowly moving ff to the southeast. A
replacement High 1020hpa is expected to cross Tasmania by Tuesday and reach
southern NZ as 1032 on Wednesday and then peel off to the east from
Thursday.
NZ/Tasman troughs
Highs are expected to dominate the weather pattern over NZ this week. OK for
coastal sailing.
But pattern is not OK for trans-Tasman sailing this week.
One trough in the Tasman Sea is expected to pass by the south of NZ on
Monday,
Another trough should form off New South Wales/Tasmanian coast on
Tuesday/Wednesday then peel off to south.
Low from Coral sea expected to travel around New Caledonia on Wednesday and
then go southwest toward Queensland and fade away before making landfall.
No racing in the Prada cup until finals start on Sat 13 Feb.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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 mailto:bob@metbob.com or txt 6427 7762212
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Bob Blog

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.

Compiled Sun 24 January 2021

 

So how windy was that storm or how extensive was that calm zone that affected your last voyage?

 

If you are interested in looking at the wind flow that affected any of your voyages in the past three years then I recommend the site manati.star.nesdis.noaa.gov/datasets/SSCATData.php

This shows the latest winds as measured by the Scatterometer satellite (see en.wikipedia.org/wiki/Scatterometer). It defaults to wind vectors at 10x15 (12.5km resolution) and a map for its latest ascending and descending passes over the planet--- and you can click on this map to zoom in to data over an area 10deg lat x 15deg Long . There are gaps of “no data” between passes.

 

Note that this imagery is from the REAL WORLD, but, due to assumptions in the data conversion, isn’t 100% accurate. It is better than the data you see from the NOAA GFS computer model output that you can view on windy.com. Both show, for example, coastal wind acceleration around the North Island East cape, but the scatterometer has a better resolution. Also, the computer model is somewhat inexact with the winds over the South Taranaki bight and a lull west of Taranaki when compared with the real world as seen on the scatterometer.

 

 

One tool that is available on this web site is access to archived data near the top of the page:

The archived data (given in UTC date) goes back to 2019, so you can dial up the imagery and see the details of the winds that affected your last voyage. Plug in the date of your choice and press “Get Images”.

 

The website also offers access to the ASCAT data which dates back to 2007, but this satellite has about 50% of no-data between passes so is less useful.

 

The Tropics

The southern Indian Ocean remains the basin of attention. Cyclone ELOISE made landfall over Mazambique yesterday, and another cyclone (13S) is forming over the ocean. There are some zones of high potential for tropical cyclone formation around north Australia, stretching to New Caledonia and Fiji.

 

The active part of Madden Julian Oscillation (MJO) is expected to travel across the South Pacific over the next few weeks , increasing the potential of tropical cyclone formation.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is spread out from Coral Sea to Vanuatu to Fiji and intensifying. The risk of a tropical cyclone forming during the next week or to is HIGH and a tropical low is expected to form between Vanuatu and Fiji by mid-week.

 

Subtropical ridge (STR)

HIGH 1018 in north Tasman Sea is expected to fade away over northern NZ by Wednesday .

New HIGH is expected to spread east along 45S past the south of Tasmania on Wednesday and reach southern NZ by the weekend.

 

NZ/Tasman troughs

Strong westerly flow over southern NZ on Monday and Tuesday.

Trough is expected to cross NZ on Wednesday followed by a southerly flow on Thursday.

For the start of the Prada Cup semi-finals on Fri-Sat-Sun 29-30-31 Jan, the outlook is for a SW wind on Friday, then NE winds on Sat and Sun.

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

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

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

Bob Blog 17 Jan 2021

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.
Compiled Sun 17 January 2021

The state of the ENSO
La Nina is at its peak

The tropics drive our weather pattern. El Nino and La Nina are opposite ends
of a swing of an identifiable tropical influence on our seasonal weather.
The La Nina, caused by cooler than normal seas along the equatorial eastern
pacific, shifts the subtropical ridge away from the equator and strengthens
the trade winds.
The El Nino, with warmer than normal seas, draws the subtropical ridge
closer to the equator, weakening the trade winds, and allowing the westerly
winds of the roaring 40s to get further north. Their comings and goings can
last several months, maybe over a year, and so their status can be used to
help forecast the weather for the coming season.

The Atmosphere:
ENSO = El Nino/Southern Oscillation. The main parameter we watch from the
atmosphere is the Southern Oscillation Index SOI (30 day running mean) as it
sums up the whole weather pattern over the South Pacific into one number. It
is based on the standardized difference in the barometer readings between
Tahiti and Darwin, in other words it counts the average number of isobars
between them on the weather map. When the SOI is more than plus one
(standard deviation from its mean) for more than a month we call it a LA
NINA event, and when it stays more than minus one we call it an EL NINO
event.
The SOI has been positive since last August and is now reaching as high as
plus 2.

The Ocean:
The sea surface temperatures in the equatorial eastern Pacific zone NINO3.4
is used as our oceanic parameter. This started going negative in May 2020
and reached a peak in coolness last November and is no slowly relaxing.
Looking at the two graphs shown here, we can conclude that the El Nino was
strongest in the ocean a few months ago and is now strongest in the isobars,
but seems to be at its peask as the oceanic temperature are relaxing.


According to the International Research Institute of the Climate Prediction
Centre,
at iri.columbia.edu/our-expertise/climate/forecasts/enso/current/, reviewing
all of the different models for forecasting the future of this La Nina, it
is expected to weaken to neutral by May 2021.

Impact on South Pacific
Trade winds should stretch further south than normal and may be more robust
than normal.
As for tropical cyclones, well looking at the sea surface temperature, the
most likely area for formation is around Coral Sea/New Caledonia.

The Tropics
The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical
Cyclone Potential is from www.ssd.noaa.gov/PS/TROP/TCFP/index.html
The southern Indian Ocean remains the basin of attention , with TC JOSHUA
drifting to the west. There are some zones of high potential for tropical
cyclone formation around north Australia and Philippines.


SPCZ=South Pacific Convergence zone.
SPCZ is spread out from Coral Sea to Vanuatu/New Caledonia to Fiji with a
weaker convergence zone from Samoa to the east.
A low south of Fiji is expected to move east along 25S to 30S, followed by a
string of lows forming south of Fiji then moving off to the southeast.


Subtropical ridge (STR)
HIGH 1016 in north Tasman sea s expected to fade away by Tuesday.
New High 1020 over Tasmania on Wednesday should move northeast across Tasman
sea and reach northern NZ over the weekend--- in time for the next two Round
Robins in the Americas Cup in the Hauraki Gulf (very light winds on the
Saturday).

NZ/Tasman troughs
Strong westerly flow over southern NZ on Monday turning NW on Tuesday.
Deep low 970hPa expected to travel across south of South Island on
Tuesday/Wednesday with associated trough over NZ. Then there is expected to
be strong SW flow and large swells on Thursday, easing on Friday.

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

Bob Blog

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.

Compiled Sun 10 January 2021

 

Clouds

Rows and floes of angel hair

And ice cream castles in the air

And feather canyons everywhere

I've looked at clouds that way

But now they only block the sun

They rain and snow on everyone

So many things I would have done

But clouds got in my way

I've looked at clouds from both sides now

From up and down, and still somehow

It's cloud illusions I recall

I really don't know clouds at all

© Joni Mitchell, June 19, 1967; Gandalf Publishing Co. (as "From Both Sides Now")

 

Basically, over the sea. clouds can be either flat (in stable air) or bubbly (in unstable air).

Flat clouds are the result of gentle large scale upward motion, such as when moist warm air from the tropics rises slantwise along a slope such as a frontal boundary.

Flat layered clouds are Cirrus, Cirrostratus, Cirrocumulus, Altostratus, Altocumulus, and, when thick enough they bring RAIN as Nimbostratus.

Bubbly clouds occur where the air has sufficient buoyancy to rise against gravity. This occurs in unstable air and on a smaller scale in time and space than stable air. Cumulus clouds can grow to towering cumulus and produce SHOWERS. These may grow into Cumulonimbus clouds that may become dangerous, producing thunder and lightning, and/or hail, or squally winds, or maybe tornadoes.

Clouds can also become wavy. These do not occur over the sea, rather they form over land, downstream of mountain.

The Latin names for clouds were introduced by Luke Howard (a Chemist) in 1802.

Isobars: The average surface atmospheric pressure is 1013.25hPa. Nearest isobar to that is 1012, and indeed it is usually the straightest isobar on the weather map. Isobars with lower numbers are generally cyclonically curved and unstable. Isobars higher than 1012 are usually anticyclonic curved with stable air.

 

The Tropics

The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical Cyclone Potential is from www.ssd.noaa.gov/PS/TROP/TCFP/index.html

 

TC DANILO continues going west across the Indian Ocean.

There are some zones of high potential for tropical cyclone formation around Indonesia and north Australia. . .

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is south of its normal position and stretches from Coral Sea to southern Vanuatu/New Caledonia and south of Fiji/Tonga with another convergence zone from Tuvalu/Samoa to the east.

A low is expected to form south of Fiji on Monday and then travel south to east of NZ North Island by Thursday and then off to the southeast.

 

Subtropical ridge (STR)

HIGH 1020 in mid Tasman Sea is expected to stay put this week --- good for trans-Tasman travel sailing west to north of 20S or sailing east to south of 35S or motoring at 30to 35S.

This High is expected to spread across central NZ on Monday and form a new centre east of the South Island that should travel east along 40 to 45S. There is expected to be a squash zone of strong winds between this High and the Low from Fiji. This squash zone should form large swells affecting eastern North Island especially on Wednesday and Thursday.

 

NZ/Tasman troughs

The Tasman High is blocking other features this week, but a passing trough should get across the South Tasman Sea on Thursday and deepen into a low south of South Island by Saturday—pushing the High off to the northeast, and replacing it with a west-southwest flow

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

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

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

Bob Blog

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.

Compiled Sun 3 Jan  2021

 

REVIEW OF THE LAST MONTH (December 2020)

Sea Surface temperature anomalies as at

www.weatherzone.com.au/climate/indicator_sst.jsp?lt=global&lc=global&c=ssta

 

La NINA (the cool eastern equatorial Pacific) continues and there are warmer-than-normal patches in the Southwest Pacific, notably in the Coral Sea. This has the makings of an active cyclone season, especially near the dateline.

To see how the annual weather cycle and the seasons are working out, we can check the average isobar maps for past 30 days and their anomaly from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

The sub-tropical ridge in the southern hemisphere has strengthened and shifted south. Not sure why, but the Arctic area has flipped from below normal to above normal pressure. Interesting.

Zooming into the NZ area, and comparing monthly anomalies from last month with now, the sub-tropical ridge has gone south - the 1010 isobar over NZ has drifted from 40S to 47S and over Vanuatu area it as drifted from 10S to 18S.

 

The Tropics

The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical Cyclone Potential is from www.ssd.noaa.gov/PS/TROP/TCFP/index.html

 

TC DANILO is in the Indian Ocean.

There are some zones of high potential for tropical cyclone formation around eastern Indonesia/Papua New Guinea this week, and a moderate zone near New Caledonia/Fiji. .

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ stretches from Coral Sea to Vanuatu to between Fiji /Tonga, with another convergence zone north and east of Samoa. SPCZ is active and a Heavy Rain warning is in force for Fiji with a flood warning for low-lying areas.

A trough is affecting the Fiji area for next few days and should spread onto Tonga by mid-week. Another trough is expected to affect New Caledonia for next few days. If you are in these areas , then may as well stay put this week.

 

Subtropical ridge (STR)

HIGH 1018 in mid Tasman Sea is expected to spread onto northern NZ on Tuesday and Wednesday.

 

NZ/Tasman troughs

Low 1008 over South Island had a cut-off low aloft but this is now fading and the surface low should finally move off to southeast on Monday.

Low 1004 is expected to form offshore New South Wales on Monday and then travel southeast to south of South Island 998hPa late on Wednesday.

Another low 1004 should form in trough of first low in around Lord Howe Island on Wednesday and then travel southeast onto central NZ over the weekend.

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

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

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