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

27 May 2018

Bob Blog 27May 2018

WEATHERGRAM

YOTREPS

Compiled Sun 27 May 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.

TROPICS

In the Arabian Sea MEKUNU has made landfall onto Oman and faded away. As seen at metoc.navy.mil/jtwc/products/io0218.gif

ALBERTO has started toff ten north American Cyclone season slightly earlier than normal and is referred to as a Subtropical STORM  From www.nhc.noaa.gov/storm_graphics/AT01/AL012018_5day_cone_no_line.png

And the Indian Monsoon is arriving on time in SE parts of Colombo (As seen at windy.com)

 

If we compare the past week’s rain map with the previous week we can see the cyclonic activity in the Arabian Sea and Florida/ Caribbean area  – 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 put from Solomon island to Northern Vanuatu to south of Fiji to Southern Cooks.

A trough with extra wind and rain is expected to travel east across Fiji/Tonga/ Niue on Monday UTC 

Accumulated rainfall for next week  can be seen at windyty.com

 

Subtropical ridge (STR)

The STR continues to be weak in the South pacific this week.

The HIGH over the southern Tasman Sea on Monday is helping to feed a polar outbreak by shovelling polar air northwards.

This HIGH should travel eastwards across NZ on Tuesday/Wednesday/Thursday.  And then intensify as it travels off to the east of NZ late this week.

 

Around Tasman Sea, NZ/Aus to tropics

Some people have been referring recent NZ weather to be a “false spring” with periods of warmth and now a polar outbreak.  However, the nights are noticeably getting longer, and the transition from autumn weather systems to winter weather systems is now complete, with cold fronts reaching as far as 25south.

This week a LOW is expected to form in the south Tasman Sea on Wednesday and the its progress to the east is expected to be delayed by the high on its eastern flank.  This Low is finally expected to travel east across central NZ, with wind and rain, on Mon 4 June, a public holiday in NZ.  

Those travelling to tropics should be able to get far enough north with a Monday departure so as to get to north side of trough when it arrives this weekend, an Ok voyage.   However, a Tuesday or Wednesday or Thursday departure may start in light winds and get caught by the northerly winds ahead of the next trough from Thursday, or in the next trough itself on Sunday/Monday.

 

New Zealand to French Polynesia

A departure by Wednesday this week looks good. And should be able to ride to polar outbreak.

 

Galapagos /Marquesas

From Galapagos area to Marquesas, departure can be any time this week. Best path for wind and current is to motor/sail to south of 4S then go to 6S 110W, then follow the current to 7S 128W then go direct. 

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

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 text only (and translator) is at weathergram.blogspot.co.nz.

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

bob@metbob.com or txt 6427 7762212

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

 

Bob Blog 27 May

WEATHERGRAM

YOTREPS

Compiled Sun 27 May 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.

TROPICS

In the Arabian Sea MEKUNU has made landfall onto Oman and faded away. As seen at metoc.navy.mil/jtwc/products/io0218.gif

ALBERTO has started toff ten north American Cyclone season slightly earlier than normal and is referred to as a Subtropical STORM  From www.nhc.noaa.gov/storm_graphics/AT01/AL012018_5day_cone_no_line.png

And the Indian Monsoon is arriving on time in SE parts of Colombo (As seen at windy.com)

 

If we compare the past week’s rain map with the previous week we can see the cyclonic activity in the Arabian Sea and Florida/ Caribbean area  – 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 put from Solomon island to Northern Vanuatu to south of Fiji to Southern Cooks.

A trough with extra wind and rain is expected to travel east across Fiji/Tonga/ Niue on Monday UTC  

Accumulated rainfall for next week  can be seen at windyty.com

 

Subtropical ridge (STR)

The STR continues to be weak in the South pacific this week.

The HIGH over the southern Tasman Sea on Monday is helping to feed a polar outbreak by shovelling polar air northwards.

This HIGH should travel eastwards across NZ on Tuesday/Wednesday/Thursday.  And then intensify as it travels off to the east of NZ late this week.

 

Around Tasman Sea, NZ/Aus to tropics

Some people have been referring recent NZ weather to be a “false spring” with periods of warmth and now a polar outbreak.  However, the nights are noticeably getting longer, and the transition from autumn weather systems to winter weather systems is now complete, with cold fronts reaching as far as 25south.

This week a LOW is expected to form in the south Tasman Sea on Wednesday and the its progress to the east is expected to be delayed by the high on its eastern flank.  This Low is finally expected to travel east across central NZ, with wind and rain, on Mon 4 June, a public holiday in NZ.  

Those travelling to tropics should be able to get far enough north with a Monday departure so as to get to north side of trough when it arrives this weekend, an Ok voyage.   However, a Tuesday or Wednesday or Thursday departure may start in light winds and get caught by the northerly winds ahead of the next trough from Thursday, or in the next trough itself on Sunday/Monday.

 

New Zealand to French Polynesia

A departure by Wednesday this week looks good. And should be able to ride to polar outbreak.

 

Galapagos /Marquesas

From Galapagos area to Marquesas, departure can be any time this week. Best path for wind and current is to motor/sail to south of 4S then go to 6S 110W, then follow the current to 7S 128W then go direct.  

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

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 text only (and translator) is at weathergram.blogspot.co.nz.

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

bob@metbob.com or txt 6427 7762212

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

20 May 2018

Sam is going negative

WEATHERGRAM

YOTREPS

Compiled Sun 20 May 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.

 

Weather regimes – SAM

Humans love finding patterns in things. Our orbit around the sun is so repeatable and predictable that we have “seasons”. Watching weather maps long enough, one can see that sometimes the same weather system (or extreme) may repeat in clusters. Last week I blogged about ENSO showing how flip-flops of the sea surface temperatures near the Galapagos are used to help decide if the weather pattern for the next season or so can be slotted into an El Nino or a La Nina regime. There are other cyclic anomalies on different time scales that we can use to help forecast if a weather regime may occur over the next few months.

 

Tonight, I think I’ll blog about SAM, the southern annular mode. This is a measure of the strength of the westerly winds in the Polar vortex - the ring of westerly winds that circle the planet between 50S and the Antarctic circle (66 S). The value of SAM alters the north-south movement of this vortex. A high positive value of SAM occurs when the air pressure over Antarctica are lower than normal, so that the westerly winds in the polar vortex are stronger than normal (note, the actual isobars over Antarctica are always higher than those in the polar vortex, but SAM works with the anomaly values, not the actual values). So, in a high positive SAM the polar vortex is shifted southwards, and pressures over NZ are higher than normal, with weaker than normal westerly winds and settled weather.

 

This can be seen at blog.metservice.com/Southern-Annular-Mode

 

However, when SAM is negative, the westerly winds in the polar vortex are weaker. This allows the polar vortex to spread outwards and thus northwards, so that west to southwest winds over NZ are stronger than normal.

 

SAM tends to flip-flop from positive to negative, and then to hold a phase for several weeks. When SAM jumps from positive to negative, it usually means that the polar vortex weakens, and the blob of cold air that has been sitting over Antarctica and getting colder over a number of weeks is able to burst outwards like a dam break. In other words: “a polar outbreak”.

 

I can not find any real time. or forecast data for SAM (which refers to differences  in pressure anomalies in the zone south of 50S), however a proxy of SAM is available, namely the AAO or Antarctic Annular mode (average 700hPa Z wind component 20S to 90S) as at  www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/new.aao_index_ensm.html

 

And forecast issued today shows that the AAO is about to have a negative jump later this week. This indicates a good chance of a polar blast somewhere (not necessarily affecting NZ). Looking at EC data of the surface air temperature forecast on windy and comparing Sunday with the forecast for Friday, it seems that the main change may occur around south and southeast of South America.

 

TROPICS

It was an interesting week with a tropical cyclone making landfall from the Red Sea onto Ethiopia. There’s also a tropical low in the Arabian Sea and it is expected to make landfall onto Oman, the horn of Africa, this week. And the Indian Monsoon is poised to strike a few days earlier than normal.

See timesofindia.indiatimes.com/india/monsoon-to-arrive-on-southern-coast-on-may-29/articleshow/64221885.cms

Next week a tropical low is expected to form in Gulf of Mexico and then make landfall on Florida next weekend.

 

If we compare the past week’s rain map with the previous week 

as at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

we can see the increase in activity across the Indian Ocean. There are also been a build up in activity in the NE Pacific Ocean. And the South Pacific Convergence zone has weakened and split into two.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

No tropical depressions or troughs this week. The SPCZ is expected to weaken and retreat to be just between Solomon Islands and Tuvalu, maybe as far east as Tokelau. This provides a good weather pattern for yachts seeking to go westward this week.

 

Subtropical ridge (STR)

The STR is weak in the South pacific this week, and that allows a LOW to form in a passing trough near 30S 170W on Monday UTC and to deepen and it travels off to the SE reaching a peak 995hpa near 38S 140W on Wednesday, then fade and go east. May affect traffic between NZ and Papeete, avoid.

Next HIGH is still quasi stationary around Aussie Bight this week, but expected to poke out a tongue of a ridge along 30S from Wednesday, and this should expand be a High east of NZ from Friday. No squash zones.

 

Around Tasman Sea, NZ/Aus to tropics

Disturbed SW flow. One front travelling east over NZ on Tuesday/Wednesday., with SW swells reaching 7+m in eastern Tasman Sea.

Next front travelling east across NZ on sat/Sun 26/27 May. There is a chance that a HIGH may bud off from Southern Ocean and move into Tasman Sea after this front. In which case there may be a good weather pattern for departing from NZ to the tropics around Monday 28 May. Still too far away to be sure.

The SW swells from South Tasman sea should reach New Caledonia south coast with a burst over 3m from Thursday 24 May until early next week.

 

New Zealand to French Polynesia

Avoid departing when a front s near NZ as on Tue/wed or Sat/sun, otherwise Ok to go.

 

Panama to Galapagos /Marquesas

Panama area is surrounded by active shower activity this week, and there are SW winds, so nothing favourable on offer this week. If you do motor off, go SSE to 4N 79W then SSW to 2N 80W and then west to 2N 86W.

From Galapagos area to Marquesas, departure can be any time this week. Best path for wind and current is to motor/sail to 4 South 95W, then sail to 6S 127W and then go direct.

 

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

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 text only (and translator) is at weathergram.blogspot.co.nz.

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

bob@metbob.com or txt 6427 7762212

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

 

13 May 2018

Bob Blog 13 May 2018

WEATHERGRAM

YOTREPS

Compiled Sun 13 May 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 state of the ENSO =  neutral

 

The Atmosphere:

El Nino and La Nina are opposite ends of the 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 the El Nino, with warmer than normal seas, draws the subtropical ridge closer to the equator. 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.

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 in 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.

For the past year the SOI has been mostly around plus 0.5 to plus 1.0, consistent with a weak but rather persistent La Nina. The subtropical ridge line has been further from the equator than normal, and trade winds were stronger than normal, but are now close to normal.

However, over the past month, the SOI has settled into a near zero state, and has a NEUTRAL status.

Neutral conditions may be as seen at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekly

(Note that in this graph on the vertical axis 10 = 1 standard deviation)

 

The Ocean:

NINO3.4 is a region in the eastern equatorial Pacific Ocean that acts as a heat storage area during an El Nino or becomes cooler than normal during a La Nina. This plays with the heat budget of the atmosphere and thus with the weather patterns.

At the farmonline web site we can see the trend in the sea surface temperature in the NINO3.4 area. The diagram shows the weekly temperature anomalies since Jan 2015, with the El Nino of 2015 looking like a hump on a camel. Since then there has been a cool period late 2016/early2017, then a warm period until July 2017, and then a cool period. That cool period seems to be coming to an end now, and the sea surface temperature are near normal.

Near normal as seen at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=nino34&p=monthly

Waters beneath the surface are slightly warmer than normal

 

The International Research Institute of the Climate Prediction Centre compiles data from several ENSO prediction models. The model predictions for the Nino 3.4 SST anomaly is that the seas ae likely to gradually WARM during the rest of this year, but the mean of the predications has only warming to 0.5 above normal--- not enough to be called an El NINO event (but closer to it that we have been for a while).

See CPC/IRI predictions at iri.columbia.edu/our-expertise/climate/forecasts/enso/current/

 

Latest SST anomaly map shows the remains of a large blue pool of cooler water across the central equatorial Pacific. Also, there are warmer yellow waters appearing around the Galapagos.

See the Sea surface temperatures across the Pacific on 10May at www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html

 

TROPICS

 

There are a few tropical depressions in the north Pacific, but they seem to be weak this week.

The rain map for the past week shows peak rainfall occurring around Indonesia and Micronesia – see rmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

No tropical depressions or troughs this week. The SPCZ is expected to remain strong over Solomon Islands and then weak across Tuvalu and Tokelau, then strong from around Niue to Southern Cooks.

 

Subtropical ridge (STR)

HIGH to east of NZ is expected to remain quasi-stationary near 30S shifting from 160W on Monday to 140W by end of the week.

Next HIGH is expected to remain quasi stationary around Aussie Bight this week and may poke out a tongue of high pressure across the north Tasman sea late in the week. There should be a squash zone of strong SE winds forming in the northern coral sea from Tues 15 Nay, in response to this HIGH, and this squash zone may extend to New Caledonia/ southern Vanuatu next week.

 

Around Tasman Sea

Low 1 in mid Tasman Sea on Monday is expected to travel onto central NZ on Wednesday.

Low 2 should form southeast of Lord Howe on Wednesday and then travel onto northern NZ on late Thursday. After that there may be a trough passing over NZ on Sunday, and then, with luck, a swing to SW winds.

 

New Zealand to Tropics

There may be a gap between passing troughs lows with a departure from Northland on Tuesday, or late Friday, otherwise may need to wait until SW winds arrive next week.

 

New Zealand to French Polynesia

Northwest to westerly winds or an offer for a good start this week.

OK for sailing east, but don’t depart in the passing troughs on late Thursday.

 

Panama to Galapagos /Marquesas

For sailing from Panama, the upcoming week looks to have head winds from SW /S around 15 knots. May be better to stay put and hope for better next week.

From Galapagos area to Marquesas, departure can be any time this week. Best path for wind and current is to motor/sail to 4 South 95W, then sail to 7S 130W and then go direct

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

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

Feedback to bob@metbob.com or txt 6427 7762212

I’m on Facebook at www.facebook.com/metbobnz/

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com, Subscribe/unsubscribe at the bottom.

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

 

06 May 2018

Bob Blog 6 May 2018

WEATHERGRAM

YOTREPS

Compiled Sun 06 May 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.

ONE addition to last week’s Blog:

In French Polynesia: the PolyMagNet (Polynesian Magellan net) takes reports from vessels under way and is a good source for information exchange about anchorages, weather, services, events and activities. Twice daily on 8173 kHz at 18:00 and 4:00 UTC. Most of the 7 net controllers have been around French Polynesia for many years and have plenty of info to share with new arrivals.

 

Weather trend over the last month.

Sea Surface temperature anomalies as at end of April may be seen at www.ospo.noaa.gov/data/sst/anomaly/2018/anomnight.4.30.2018.gif

The SST anomaly image is now noticeably different from what it was at end of March.  With sea temperature sin the south Tasman Sea near normal, and the cool anomalies near the equatorial East Pacific much weaker than what they were.  In fact, some warm anomalies are starting to show near the Galapagos

The Gulf Stream off the east coast of North America continues to stand out as being much warmer than normal; this extra heat continues to energize storms over the northeast of North America into their spring.  Warm anomalies continue over much of the North Pacific, and that may be an indicator to a busy cyclone season there later this year.

During April there really was only one cyclone KENI which started near Vanuatu and peaked near Kadavu in southern Fiji. There was intense monsoonal rain over Fiji during the fortnight ahead of KENI, and the cyclone managed to take those clouds away. A full time-map of the season’s cyclones can be seen on wikipedia at en.wikipedia.org/wiki/2017%E2%80%9318_South_Pacific_cyclone_season

To see how the annual weather cycle and the seasons are working out, take a  look at the average isobar maps and their anomalies at www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

The averaged-isobar map shows that subtropical ridges are looking good in both hemispheres.  The anomalies show that the HIGHS which were affecting NZ have been replaced by lows. The 1015hP (between blue and white) isobar has retreated during the last month to a smaller area over the NZ region, and can be seen shifting northwards over Australia.

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

This rain map shows the “extra convergence zone” stretching from just south of Galapagos westwards to NW of Marquesas, but weaker than normal.  It also shows very dry conditions for the past month over northern Australia, and dry in Brazil.

 

 

TROPICS

The MJO oscillation is traveling across northern Australia this week, but is weak and not expected to do much.There is a weak tropical depression between Philippines and Micronesia and it is expected to shift off to the north this week.

 

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to remain close to where it was last week, with  its activity focused on a line stretching from Solomon Islands to Rotuma to Samoa to Southern Cooks.

Convection between Galapagos and Marquesas is expected to continue to weaken.   

Accumulated rainfall for next week from windyty.com.

 

Subtropical ridge (STR)

HIGH in the central Tasman Sea on Monday is expected to slowly travel is expected to slowly travel across northern NZ on Wed and Thursday, and then off to the northeast of NZ from Friday.  There is likely to be a squash zone of enhanced trade winds on the north side of this HIGH from Southern Cooks to Tonga early next week.

Around Tasman Sea

Deep Low from the Southern Ocean is expected to whip past southern NZ on Monday /Tuesday /Wednesday with strong westerly winds and large swells.

Another Low is expected to visit Tasmania on Thursday and then travel northeast into the central Tasman sea on Sunday and Monday. Avoid.

This Low should bring a S/SW wind change to the Southport to Noumea route on Sunday/Monday 13/14 May. The SE winds should return to the Noumea area by end of Tuesday 15 May, but it may be a few weeks before this pattern repeats, so this opportunity may be best on offer for a while for sailing from Southport to Noumea.

 

New Zealand to Tropics

Looks Ok for departures until Tuesday. After that, voyages going north  are likely to encounter northerly winds ahead of the next incoming trough by Friday.

New Zealand to French Polynesia

Light winds over northern NZ until Wednesday, and then northerly winds, which may be somewhat wet, but ok for sailing east.

 

Panama to Galapagos /Marquesas

For sailing from Panama, the upcoming week looks to be just light winds as far as 5North and then  SSW to SE winds.  Difficult.

From Galapagos area to Marquesas, departure can be any time this week. Best path for wind and current is to motor/sail to 4 South 95W, then sail to 7S 130W and then go direct

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

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

Feedback to bob@metbob.com or txt 6427 7762212

I’m on Facebook at /www.facebook.com/metbobnz/

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com.

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

 

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