BOB BLOG 9 Aug

WEATHERGRAM

YOTREPS

Issued 9 August 2015

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.

  

30 day actual and anomaly wind map may be seen at http://www.esrl.noaa.gov/psd/map/images/fnl/sfcwnd_30b.fnl.gif

This shows the wind anomalies for the last month to be typical of an El Nino cycle—with extra westerly winds along the Pacific Equator acting to move the sun-warmed sea to the east.  There are some quirks- the extra SW winds are over Chatham Islands rather than mainland NZ.  And that extra feed of air from Antarctica to the Aussie bight is interesting. 

 

El Nino in the ocean

Now that this El Nino is working in the atmosphere it is giving positive feedback to the heat that is being stored in the seas of the Eastern Equatorial Pacific.  This can be shown by looking at the sea-surface temperatures of the target areas, the NINO 3.4 index.   Over the past few weeks this has intensified.  It is now reaching levels last seen in 2010,  and has a long way to go to reach the extremes of 1998 (so don’t believe everything you may hear). 

 The Nino3.4 index since 1990s may be seen at http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=nino34&p=monthly

This current El Nino is expected to intensify until around November and then weaken, but it is not expected to drop below its current strength until around March 2016.

 

TROPICAL TOPICS

There are two tropical cyclones at present Hurricane/ Typhoon SOULDELOR has grown to become arguably the largest storm so far this year and is now inland over mainland China after crossing Taiwan.

To the north of SOULDELOR we have MOLAVE east of Japan  It seems that the Hawaiian area is getting sideswiped around once a week: This week we have Hurricane HILDA heading for the north side of Hawaii.

So far the North Atlantic is having a quiet summer—most of the activity is in the Pacific this year, possibly because of the warmer sea temperature.

 

The weekly rain maps over the past two weeks show the intense rainfall from these tropical cyclones, and even more intense and widespread rainfall in the monsoon over Myanmar, spreading across Thailand and towards Malaysia.

Weekly rain signatures for past two weeks may be seen at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

 

SPCZ=South Pacific Convergence zone.

Trough attached to SPCZ is tonight crossing Tonga and by Wednesday UTC (Tuesday local0 is expected to be weakening between Niue and Palmerston Islands. It has NE winds on its eastern side, some squalls with its main wind change, and is followed by southerly /SW winds.  It should continue east, reaching Tahiti on Saturday UTC (Friday local).

A trough/front from the Tasman Sea is expected to move onto New Caledonia on local Friday.

Try and pick your Island hopping to happen in-between these troughs.

 

STR= Sub-tropical Ridge

The weak ridge that is in the Tasman Sea tonight delivering a chilling southerly to NZ  is expected to travel across NZ on Tuesday and Wednesday, then further east along 30 to 45S east of NZ on Thu/Fri/Sat,  this is expected to be a frosty high.

 During this week a BFH, Big fat high, is expected to travel slowly across the interior of Australia, and finally enter the Tasman Sea early next week.

 

NZ

On Monday and Tuesday there are still a few disturbances in the southerly flow that may affect the east coast, but conditions look Ok for departing from Northland.

After a short period of light winds Wednesday morning, the northerly winds ahead of the next trough are expected over NZ by late Wednesday.

This trough is expected to start deepening into a LOW SE of Sydney on Wednesday night and then travel east crossing the Auckland area on Saturday night, and is expected to be squally and followed by a few days of squally W/SW winds until at least Mon 17 August. 

SO best days for anyone planning to go to the tropics are Monday and maybe Tuesday.

 

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