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

15 April 2018

Bob Blog for 15 April

WEATHERGRAM

YOTREPS

Compiled Sun 15 April 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

IRIS: There were still convective squalls in the remains of IRIS in the Coral sea until last Thursday, about four weeks after it started.  

KENI: Tropical cyclone KENI travelled over Kadavu on Tuesday 10 April, and then went southeast out of the tropics.  As it left the tropics, KENI was captured by the jetstream belonging to an approaching upper trough.  This ripped the upper part of the tropical feature to bits, but the surface low wasn’t affected much, as evidenced by (modelled) isobars around the centre.  This is shown in an animation I took using Windy, looking at the EC model. 

 To see this, visit youtu.be/6c4EP-NcrcI, entitled KENI and the Jets.

This animation also shows the squally trough that crossed North Island on Tuesday 10 April and how clouds in this feature were able to bring twisting winds and tornadoes to New Plymouth, and, a few hours later, were able to bring jetstream like-winds downwards as damaging downbursts that fanned Auckland on Tuesday evening. The peak gust at the airport was over 80 knots and the gale lasted around 14 hours. My email server was knocked offline for a day.  Anyone who sent me an email last Wednesday was sent a bounce message that may have said things like “domain doesn’t exist” or even “has been blacklisted”. Charming, I don’t think.

Tropical Outlook for remainder of the month:

The next MJO (or pulse of enhanced convection) is still building in the Indian Ocean and now looks like it will reach Western Pacific towards the end of April.   By then the nominal cyclone season will be ending. And until then it looks as if the South Pacific should be in a period of quieter convection. So, the signs are now pointing to an end of this cyclone season in the South Pacific (but North Australia may get one more opportunity towards end of the month). 

Now that cruising sailors are preparing for their voyages to the tropics, if you wish to join an organised rally, well the Down Under crowd are in full swing arranging the GO EAST Cruisers rally from the Gold Coast (starting around 14 May) to New Caledonia.  For more info see www.downunderrally.com/about-go-east/ The Island Cruising New Zealand are organising a rally from Opua to Tonga, but registration for this is now full. If you’d like to join the waiting list then see www.islandcruising.co.nz/?page_id=3896

 

WEATHER ZONES

SPCZ

The SPCZ is weaker and thinner than last week, and is expected to stretch from eastern Solomon Islands, to Wallis/Futuna and between Samoa and Tonga to Austral islands.

There is still an “extra convergence zone” around 5 to 8S from SW of Galapagos around 100W to northeast  of the Marquesas around 120W.

Subtropical ridge (STR)

HIGH between Fiji and NZ tonight is travelling away to east along 30S and should fade away by Wednesday.

Next HIGH is expected to form in central Tasman Sea on Tuesday and Wednesday and then travel northeast across northern North Island by the 21/22 weekend.  This system should flatten the large swells that are in the Tasman Sea at the start of the week, so that there may be a reasonable opportunity for some trans-Tasman sailing.

And, now that these Highs are travelling east along 30 to 35S, this offers a reasonable opportunity for vessels seeking an opportunity to sail from NZ to French Polynesia.

 

Around Tasman Sea

Some deep lows are expected to be travelling east along 50S in the Southern Ocean, so there should be an enhanced westerly flow across central and southern NZ this week.  The Southern Alps are consequently expected to get more rain than the SPCZ.

Panama to Galapagos/Marquesas

For sailing from Panama,  there is expected to be some moderate northerly winds on Tuesday/Wednesday/Thursday.   After that the winds are likely to switch to light southwesterly.  So, if you are waiting to go, take this opportunity.

As from getting from Galapagos to Marquesas this week, first motor sail to around 5S 94W (may also find a tail current), then can sail direct, but that “extra” convergence zone continues to straddle 5 to 6S from about 100W to 120W. Something to avoid.

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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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08 April 2018

Bob Blog 8 April

 

WEATHERGRAM

YOTREPS

Compiled Sun 8 April 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 of my blog followers, who uses saildocs to receive this weathergram, informed me last week that he received a spam email using my email address bob@metbob.com. Has anyone else received anything?

 

Fifty years ago, on Tuesday 10 April, a storm from the tropics met with a cold front just off Wellington and re-intensified. As a result, the Inter-island ferry WAHINE sunk and 51 lives were lost that day. Our house lost its chimney. The storm was terrifying and tragic but also awesome and awful. It inspired me to study weather as a career.

See nzhistory.govt.nz/culture/wahine-disaster

 

For those of you who are now planning to depart Australia or NZ for the tropical Islands (after the cyclone season) and would like as assisted passage: here is some good news:

 

Island Cruising New Zealand are organising a rally from Opua to Tonga. Sadly the registration for this is now full, but if you’d like to join the waiting list then see www.islandcruising.co.nz/?page_id=3896

 

And the Down Under crowd are in full swing arranging the GO EAST Cruisers rally from the Gold Coast starting around 14 May  (well after the Commonwealth Games)  to New Caledonia. For more info see www.downunderrally.com/about-go-east/

 

So, when will this cyclone season finish?

 

During the last week of March and first few days of April an MJO event travelled across the South Pacific. An MJO event is the passing of a burst of tropical convection, called a Madden Julian Oscillation or MJO. This has now gone, but there is still some “left over” tropical cyclone activity sorting itself out (see below). The interesting thing is that some computer models are forecasting the MJO oscillation to travel more quickly that normal around the world so that the next one may reach South Pacific in late April, perhaps triggering another cyclone. There does seem to be a lot of variation in the MJO models— and if the next MJO is weak or arrives after late April, then that increases the chances that this is the last week of cyclone activity for the season.

 

MJO phase may be seen at www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/forca.shtml

 

TROPICS

After three weeks, IRIS is now fading away in the Coral sea. It still has a low-level circulation of wind, but that’s about all. Associated onshore winds on the south of IRIS have been bringing showers to the Gold Coast for the Commonwealth Games. That’s normal weather for them.

 

Near 17S 170E, around 100 miles ENE of Port Vila is tropical depression TD13F (Fiji Met) or 17P (Guam) continues to be a worry. Its central pressure is 998hPa, and nearest barometer at Port Vila is this evening rising rather than falling.

However, the system has persistent convection and is well placed for development and may well get named soon. It is currently doing a loop and is expected to travel southeast, skirting Fiji on Tuesday.

 

Fiji has been experiencing monsoonal rain during the past week with flooding in Labasa and Western division, and two dead, one missing. If this depression does visit Fiji over next few days it will be most unwelcome- and bring some wind as well as further rain— a week or so after JOSIE’s Easter visit.

See www.radionz.co.nz/international/pacific-news/354442/two-dead-one-missing-in-fiji-as-bad-weather-continues

 

A comparison of the weekly rain map trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

from last week with the previous week shows IRIS in the Coral Sea and the monsoonal rain over Fiji. There has also been a river of moisture extending from west of Hawaii to the USA west coast, a “pineapple express”. The “equinoctial convergence zone” between south-of-Galapagos and north-of-Marquesas is still there.

 

What is a Pineapple express? see denver.cbslocal.com/2018/04/07/pineapple-express-northern-california/

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is still intense and is expected to persist over Fiji to Samoa to Southern Cooks/French Polynesia his week. Avoid

 

Subtropical ridge (STR)

HIGH forming to NE of NZ on Monday is expected to travel off to the east along 35 to 40S this week.

Next HIGH is different, because it has budded off the ice shelf and the southerly winds on its leading edge are expected to shovel cold air onto New Zealand on Tuesday and Wednesday, dropping air temperatures to lowest so far this year. This HIGH should travel north across the Tasman sea on Wednesday and then east along 30S to north of NZ on Thursday and Friday.

Third HIGH this week is expected to form in south Tasman sea on Thursday and travel onto northern NZ by Saturday.

 

Around Tasman Sea

By mid -week the isobars are likely to be southerly from 60S to Fiji/17S. This cold outbreak is likely to be accompanied by large southerly swells from the Southern Ocean, well over 5 metres in places, but with a long period. It may trigger three smaller lows.

Another intense front is expected to cross southern NZ on Thursday and deepen into a LOW east of NZ on Friday 13th.

It isn’t really a good week from departing NZ, but those Highs in the Tasman Sea may allow a reasonable voyage between Australia and NZ.

 

Panama to Galapagos /Marquesas

Only light variable winds are forecast between Panama and Marquesas this week (and next week). The “equinoctial” convergence zone continues to straddle 5S from about 95W to 120W. Something to avoid.

For those trying to get from Galapagos to Marquesas, motor sail to 5S 95W and then go direct, may need to drop to 6S at times to avoid convection.

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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,

To unsubscribe, send a reply email saying LEAVE.

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01 April 2018

Bob Blog 1 April

WEATHERGRAM

YOTREPS

Compiled Sun 1 April 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 trend over the last month.

Sea Surface temperature anomalies as at end of March may be seen at www.ospo.noaa.gov/data/sst/anomaly/2018/anomnight.3.29.2018.gif

The SST anomaly image is much the same as t beginning of March, it still shows cooler than normal seas along the equatorial East Pacific, but somewhat weaker.

The Tasman sea warm zone, which has been there since November and which has been breaking records, is still there.  Looks like it may prolong autumn over NZ.

And the Gulf Stream off the east coast of North America continues to stand out as being much warmer than normal; this extra heat has energized storms over the northeast of North America, bringing regular winter snow and floods to Boston. Looks like there are more to come.    

South Pacific Cyclones during March have started near Vanuatu area. HOLA wen t SE, LINDA went south, IRIS went SW and bounced off the jetstream and is now in the coral Sea. And the most recent, JOSIE, has brought killing rains to western Fiji and is expected to go SE then SSE.

 

The cyclones we have so far this season my be seen on  time line 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 from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

The low pressures over Europe has encourages cold easterly winds, and the above maps show that this anomaly stretches from Siberia to Boston.  Ouch.

The anomaly map shows that lows are likely to form in the Micronesia to Hawaii area.

The subtropical ridge over the South Pacific has stayed in much the same place and intensified, typical or early autumn.  The 1015hP (between blue and white) isobar now covers all of South Australia and Tasman Sea.   Isobars southwest of NZ are closer together, an indication that the westerly winds of the roaring 40s are intensifying.

 

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

In the Pacific, the drier than normal zone along the equator is typical of a La Nina episode.

 

TROPICS

IRIS lost its upper clouds in a jetstream last week, but its lower circulation was able to hold together and was diverted northwards over warm Coral Sea.  It has rejuvenated, and the label IRIS is good enough to refer to this entity as it may re-intensify. It is expected to meander SW then NW this week but not expected to make landfall. It contains squally rain.

 

JOSIE has been bringing heavy rain to Fiji in the days leading into Easter and was named on Easter Saturday.  Its rain has brought a death toll of at least 2, and 3 missing in Fiji so far:fijitimes.com/story.aspx?id=440188

It is expected to travel SE and fade well to east of New Zealand.

 

JELAWAT formed over Micronesia during last week and is traveling NE into the North Pacific.

A comparison of the weekly rain map from last week with the previous week shows the path of the cyclones and some heavy rain north of Hawaii.  The “equinoctial convergence zone” between south-of-Galapagos and north-of-Marquesas is still there.  See trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is reforming on the back end of JOSIE, covering southern coral sea and northern Vanuatu /Fiji. with an arm extending to Southern Cooks.

Another tropical Low is likely to form over Vanuatu on Thursday/ Friday and follow JOSIE to south of Fiji during weekend of 7 and 8 April.

 

Subtropical ridge (STR)

HIGH over northern NZ today Sunday is expected to travel off to the east between 35 and 40S.  

New HIGH is expected to travel across southern New South Wales on Wednesday and stall in the central Tasman Sea for the remainder of the week.  This High should steer JOSIE clear of NZ.

 

Around Tasman Sea

Between those two Highs, a FRONT is expected to travel over South Island on Monday and fade over North Island on Tuesday.  A more intense front is expected to travel over NZ early next week around 9 and 10 April.

 

Panama to Galapagos /Marquesas

Today’s data is showing that the recent period of good winds for departing Panama is now expected to be replaced by light winds from around mid-week.   The coming period of light winds may last for a while, at least until end of next week.

The “equinoctial” convergence zone continues to straddle 5S from about 90W to 120W. Something to avoid.

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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.

Or, if email wasn’t from WordPress then send a reply email saying LEAVE.

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