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

28 January 2018

TROPICAL CYCLONE FEHI

Tropical cyclone FEHI was named this afternoon .
According to Fiji Meteorological Service.
 TROPICAL CYCLONE FEHI CENTRE {[991HPA]} CATEGORY 1 WAS ANALYSED NEAR 19.0S 161.5E AT 282100UTC .
 POSITION FAIR BASED ON HIMAWARI 8 EIR AND VIS IMAGERY AND PERIPHERAL SURFACE REPORTS.
TROPICAL CYCLONE FEHI MOVING SOUTH-SOUTHEAST AT ABOUT 10 KNOTS.
MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE CENTRE ESTIMATED AT ABOUT 35 KNOTS.
Track map is at www.met.gov.fj/aifs_prods/65661.html

Regards
Bob

Bob Blog 28 Jan 2018= 1924+94

WEATHERGRAM

YOTREPS

Compiled Sun 28 January 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.

Shorter than normal edition tonight as I’ve been helping my mum celebrate her 94th Birthday. Yeah!

 

TROPICS

There is an MJO period of expected extra convection traveling east across northern Australia into Coral sea area this week and next week, and this is raising the potential for Tropical Low development to HIGH over next few weeks.

There is a high chance that on Monday TD 06F/08P (now 994hPa near 17S 161E or about 450 n miles northwest of New Caledonia) may develop into a named Topical cyclone— It seems to be moving SSE maybe SE at present and is expected to travel south into the Tasman Sea and weaken and finally cross southern/central NZ on Thursday and Friday mainly as a real-wet rain depression and mainly rain for the southern lakes (where it is needed), and still with some wind.

Latest discussion about this feature is available at www.met.gov.fj/aifs_prods/20036.txt

 

In the Indian Ocean TC CEBILE is traveling west to southwestwards near Diego Garcia,

 

Looking at the weekly rain maps, at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, we can see that the main convective rain over the past week has shifted from the equatorial Indian Ocean to the northern Australia and Coral Sea region.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is active in the Coral to Tasman Seas with TD 06F/08P.

It is also increasing active in the zone from northern Vanuatu to Rotuma (maybe not Fiji) to northern Tonga to Niue, with more tropical lows likely.

Tropical accumulated rainfall for next week may be een at windyty.com

 

Subtropical ridge (STR)

HIGH to east of NZ o Monday should travel steadily east along 40S off to the east this week,

Next High is expected to travel from Aussie Bight to south of Tasmania along 48South on Sat/Sun 3/4 Feb.

 

Around Tasman Sea

The main factor this week is to avoid the wind and rain of TD 06F/08P. Avoid

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21 January 2018

Bob Blog 21 Jan 2018, LA NINA now relaxing

WEATHERGRAM

YOTREPS

 

Compiled Sun 21 January 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 = La Nina now relaxing

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The Atmosphere:

El Nino and La Nina are opposite ends of an identifiable tropical influence on our seasonal weather: the ‘La Nina’ is related to cooler than normal seas along the equatorial eastern pacific. It shifts the subtropical ridge away from the equator. The ‘El Nino’, with its 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 forecast the weather for the coming season.

 

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 normalized difference in the barometer readings between Tahiti and Darwin, in other words the placement of isobars 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.

 

In late 2017 there was a surge of the SOI to over plus one and into LA NINA territory in October and November. But during December and January it has relaxed and is now very near normal. Maybe this means that the extremes weather events we have seen in the past few months will now also relax.

A relaxing LA NINA is 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, and then a warm period around mid-2017. We are now in a cool period again. And in the past few months it has been as much as 1 deg C below normal—a LA NINA, still at work in the ocean.

A Continuing La Nina in the ocean as seen at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=nino34&p=monthly

 

Looking at the sea temperature anomalies along a transect of the equatorial Pacific shows that there is a plume of warmer sea at depth in the western Pacific travelling eastwards and warming the cooler surface waters of the eastern Pacific from below.  This transect may be seen at www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/figure04.gif

 

The International Research Institute of the Climate Prediction Centre compiles data from several ENSO prediction models. The early January combo probability forecast issued early January shows that the likelihood of La Nina (red bars in the graph) is expected to drop below 50% by MAM = March April May, and the outlook is for a period of neutral influence from the tropics (similar to background climatology as given by the grey line). See

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

 

Latest SST anomaly map shows a weakening in the extent and intensity of the cooler eddies along the equator. Note the warmer than normal Gulf stream of NE America, north of 35S (but cooler than normal further south). In the NZ region the warmer than normal central Tasman Sea is a potential source of energy that may help activate mid-latitude depressions over the next month of two. Sea surface temperatures for 18 Jan may be seen at www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html

 

TROPICS

TC BERGUITTA is fading away near 30S 50E to south of Madagascar. There are a few tropical depressions around but nothing more serious at this stage.

There is an MJO period of expected extra convection that is expected to travel across northern Australia this week and into the western pacific in early February. This may trigger some tropical developments near Cocos Islands rom Wednesday, and in the heat trough of northern Australia by the end of this week, and perhaps in the Coral Sea next week. Associated with this MGO thee is a zone of near equatorial westerly winds already in place as seen on windyty.com  ...keep an eye of these winds as they can easily help trigger tropical depressions.

 

Looking at the weekly rain maps from last week at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, and the week before, we can see that the main convective rain over the past week has been in the Indian Ocean and stretching to Northern Australia and around Indonesia. This cluster of extra convection is expected to make its way eastwards and start appearing in the Coral Sea area around early February.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is hovering from Coral Sea to northern Vanuatu to Samoa then to Southern Cooks, and is of increasing intensity this week, There may be a tropical low developing in western Coral Sea early next week.

 

Subtropical ridge (STR)

HIGH to east of North island is expected to continue further off to the east along 35 to 40 South.

Another HIGH is expected to form in central Tasman Sea by end of Tuesday, and then hover there until early next week.

 

Around Tasman Sea

The remains of a trough are expected to travel onto northern NZ next few days, and fade away, but they still have some maritime Polar airmass and some cooler-than-normal air aloft, so are still able to produce isolated downpours until Tuesday with light variable winds and reasonable high isobars. A typical passing summer trough.

From Tuesday, expect a generally northerly to northeast wind-flow along the Australian eastern seaboard this week, and light variable winds/or sea breezes around NZ.

 

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“We may have all come on different ships, but we’re in the same boat now.”

Martin Luther King, Jr.

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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

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14 January 2018

Bob blog 14 Jan 2018

WEATHERGRAM

YOTREPS

Compiled Sun 14 January 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.

 

Addendum to last week:

Regarding the details of the Niwa SEA LEVEL site--- the bottom graph compares the total SS in blue with the IB component in red, and last week it showed that the IB component made up most of the SS. In other words, the main component to the observed risen sea-level was the IB or inverse barometer effect, not the spring (or king) tide NOR the storm surge.  The incoming low may have brought an associated “dome of raised sea”, and as the Low travelled, so too did the dome, but the sea itself did not travel (just rose and fell as low went by).  The storm tide of piled-up and pushed-around sea water, and the king tide, provided lesser contributors.

 

In the past few days a HIGH has been crossing southern NZ with offshore winds across Foveaux Strait (Dog Island) and this produced a NEGATIVE storm surge (offshore wind)  and a negative Barometric effect lowering the sea level. The NIWA graph show that while these drops lowered the level of the sea (especially notable on the beach and over the sandbanks) to a level lower than expected by the normal “quoted tide”, they did NOT lower it to what it was at the spring tide earlier in the week.  As seen at www.niwa.co.nz/our-science/coasts/tools-and-resources/sea-levels/dog-island

  

Weather trend over the last month.

Sea Surface temperature anomalies may be seen at www.ospo.noaa.gov/data/sst/anomaly/2018/anomnight.1.11.2018.gif

The SST anomaly image shows a typical LA NINA with cooler than normal seas straddling the eastern equatorial Pacific.  Also note the warmer-than-normal zone across the Tasman Sea – this can activate any Tasman Low to produce more than normal wind/rain.  We saw an example of this on Thu/Fri 4/5 Jan and may see another (lesser) example on Tue/Wed 16/17 Jan 

To see how the annual weather cycle and the seasons are working out, take a quick look at the average isobar maps from  www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html showing the Average isobars for past 30 days and their anomaly for DECEMBER.

Note the strong three-wave pattern in the northern hemisphere with the deepest lows preferring to form near Japan, eastern North America and western Europe— this is linked to the air aloft and its jetstreams.

During December the subtropical ridge over the South Pacific shrunk, and is now focused across NZ and to west of the Andes. The 1015hP isobar shifted has spread from the Southern Ocean to the southern South Island, and from near Brisbane/Noumea to near Norfolk Island. It looks like the subtropical ridge may have given NZ an early start to summer, and now that it is fading we can expect an early start to Autumn=mist/low clouds. 

    

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

This shows that both the ITCZ and the SPCZ have an average position last month further AWAY FROM the equator than normal.  This is typical of La NIA. Interestingly in the Atlantic, the ITCZ is closer to the equator than normal—this shows that there is more happening than can be explained by just examining LA NINA.

 

TROPICS

TC JOYCE went inland to NW Australia on Friday and is now expected to get out to sea again by Tuesday and then travel south so that its rain visits SW Australia.

TC BERGUITTA is in the Indian Ocean to east of Madagascar nd expected to travel SW and then S , avoiding making landfall.

 

Looking at the weekly rain maps from last week and the week before, we can see that the main convective rain over e past week has been in the Indian Ocean and with TC JOYCE (before landfall). The cluster of extra convection in the Indian Ocean is expected to make its way eastwards and start appearing in the Coral Sea area around late January/early February.  This is called an MJO oscillation

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

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is hovering from Coral Sea to northern Vanuatu to Fiji/Tonga then to Southern Cooks, and is of weak to average intensity this week.  It is expected to become more active NEXT week, especially in the Coral Sea.

Tropical accumulated rainfall for next week may be seen at windyty.com

 

Subtropical ridge (STR)

HIGH to southeast of NZ s expected to travel northeast to 40S 170W and then east.

Next High is expected to struggle and finally get into west-central Tasman after Thursday this week, and another into southern Tasman Sea (SE of Tasmania) by Sunday 21 Jan.  These Highs should travel east – to north and south of NZ- early next week.

 

Around Tasman Sea

Trough is slowly crossing.  Low in this trough to SE of Lord Howe on Monday is expected to deepen until Wednesday and travel SSE then escape its jet and weaken and travel E/NE to Northland on Saturday 20 Jan.   Worth avoiding mid-Tasman mid-week.  And its fronts are expected to cross NZ on Tuesday night/Wednesday (occlusion/avoid) and then on Fri/Sat (cold/ho-hum).

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“It is better to be approximately right than precisely wrong.”

Warren Buffett, October 1994 (When he was richest person in the world).

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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, Click FOLLOW at bottom right.

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07 January 2018

BobBlog 7 Jan 2018

WEATHERGRAM

YOTREPS

Compiled Sun 07 January 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.

+++++++++++++++++++++++++++++++

That low over northern/central NZ last Thursday night to Saturday brought lots of wind damage and some sea-inundation damage. Indeed worth avoiding.

Yes, it did deepen quickly on Thursday, but not quite steeply enough to satisfy the definition of a meteorological bomb. Its central pressure dropped from 1000 to 981 in 24 hours at average latitude 36S, that’s 19 hPa, or 23 hPa when corrected to reference latitude of 45S. SO,it reached a max of 0.95Bergernon, not quite 1B.

 

LOW was 1000hpa at around 33S on Thursday 1am local, then LOW was 981hpa at 1am Friday near 37S.

 

The term “bomb cyclone” has been given plenty of mention in the past week because of the intense low over eastern north America directing cold air for the chilled Arctic. A good write up of how the original term was coined is at www.washingtonpost.com/news/capital-weather-gang/wp/2018/01/04/this-researcher-helped-coin-the-term-bomb-cyclone-he-did-it-to-keep-people-safe/

The lower than normal air-pressure around northern NZ last Friday lifted the sea level (inverse barometric or IB) at the rate of 1cm for every hPa below the norm of 1012 —so for 995 hPa that’s a lift of 170mm for Whitianga on Friday. The raw tides were more extreme than normal last Thursday/Friday because the full moon occurred close to perigee. The stronger NE winds completed the tri-factor and brought a large storm surge of around 200mm in on top of a larger than normal high tide and the inverse barometer effect.

Adding it all together, there was a 350mm rise to the sea level measured at the Whitianga tide gauge last Friday as seen at the NIWA plot at www.niwa.co.nz/our-science/coasts/tools-and-resources/sea-levels/whitianga-wharf. On their plot the full moon (on Tue 2 Jan) is shown as a yellow circle and the time of perigee is shown as a purple circle.

 

It should be pointed out that the low wasn’t of tropical origin and went thru its deepening process in the 30 to 35S latitude band. Basically, the surface low managed to have an upper trough move over it so that it found itself between two jetstreams—on the polar side of a jet exit and on the equatorial side of a jet entrance. In such a zone the surface air rises and is carried away by the jetstream. In this case the air was blown off faster that it could rise, and so, as air was removed from the low, its central pressure dropped “explosively” the jetstreams got energized by the release of heat as the clouds around the low turned to rain. This is a classical mid-latitude low—NOT a tropical cyclone. Once in a while (maybe as often as once per month in winter) we see a low develop like this in the Tasman Sea, but few are as serendipitous in the mixing as this one, and we haven’t seen one like this for several months.

 

Let’s hope the next one is after summer.

 

 

The Tropics:

Looking quiet in the South Pacific for the next week or two.

There are two tropical cyclones in the South Indian Ocean at present: IRVING near 15S 85E is travelling SW and expected to turn off to the south before affecting La Reunion.

And TC AVA, as seen at www.tropicaltidbits.com, is further west and fading as it travels south along the east coast of Madagascar

 

Looking at the weekly rain maps from last week and the week before, as at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, we can see pockets of intense convection over Indian Ocean and northern Australia, and an easing of activity in the Coral sea to Fiji area.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is still active between Samoa and Southern cooks, and rather weak but building over the Coral Sea and Vanuatu/Fiji/

 

Subtropical ridge (STR)

HIGH1 is expected to travel east from Tasman Sea across northern NZ on Wednesday and Thursday and then off to the east of NZ along around 30 to 35S.

The next high , HIGH2, is expected to spread east across Tasmania on Wednesday and across the South Tasman sea on Thursday and then build to northeast of NZ from Friday, moving along 40S from the weekend into next week.

 

Low crossing central Tasman Sea.

Trough is forming across the central Tasman Sea this week.

A low should form in the trough around mid-Tasman by Wednesday and then travel southeast towards the South Island on Tuesday, but is likely to stall west of the southern alps and fade away on Friday.Trough should remain in central Tasman Sea and perhaps brew another low next week.

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Feedback to bob@metbob.com or txt 6427 7762212

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

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