WEATHERGRAM
YOTREPS
Compiled Sun 12 April 2020
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.
=-=-=-=-=-=-
Volcanic eruptions:
Krakatoa in Indonesia has erupted spewing ash to 47.000ft. If there is enough ash in the stratosphere then this may reduce sunlight and drop the surface air temperature for next few days/weeks/maybe months. A Volcano in Iceland is threatening to blow, and any resulting ash cloud may affect air transport (which is already affected by Covid 190.
The state of the ENSO = neutral
It has been months since we have looked at ENSO, so here goes.
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.
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 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.
Since a brief El Nino in late September the ENSO has been neutral, but in the last week there is a trend that may bring another El Nino episode. The subtropical ridge line has recently shifted north over New Zealand, opening the door over the South Island to episodes of cold SW wind.
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 a CPC 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 May 2019. Temperature have been slightly above normal (global warming?) except for a cool period last September.
They are now reasonably steady, and below the El Nino threshold of over +1 degrees.
Neutral oceanic conditions are seen at
www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf
Waters just beneath the surface are slightly warmer than normal.
See Data for 30 March as at www.bom.gov.au/climate/enso/#tabs=Sea-sub%E2%80%93surface
The International Research Institute of the Climate Prediction Centre compiles data from several ENSO prediction models.
The model percentage predictions based on Nino 3.4 SST anomaly is that the neutral conditions are most likely (over 50%) until August and hen the seas are likely to gradually COOL later in the year, with a La Nina becoming 35% likely by the end of the year (neutral also 35, and El Nino only 20%).
CPC/IRI predictions are from iri.columbia.edu/our-expertise/climate/forecasts/enso/current/
Sea surface temperatures across the Pacific on 10 May are from www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html
Latest SST anomaly map shows a patch of cooler than normal sea near central Pacific, surrounded by slightly warmer than normal sea.
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
There are no cyclones around at present.
Cyclone HAROLD was Cat 5 over Vanuatu, Cat 4 for southern Fiji, and Cat 5 when it went slightly south of Tonga, It has produced lots of damage along or near its path, the most damaging cyclone of the season.
However, the MJO quiet cycle is expected over the South Pacific for the next few weeks and then the nominal cyclone season ends at end of the month.
WATHER ZONES
SPCZ=South Pacific Convergence zone.
After HAROLD the SPCZ is expected to be quieter than normal this week, stretching from Solomon island s to northern Vanuatu to between Fiji and Samoa to Tahiti area.
Subtropical ridge (STR)
HIGH that has been east of NZ last few days is now moving off to the east along 25S but may stall and fade near 170W for a few days.
Next HIGH is expected to move into Tasman Sea along 35S on Tuesday then go north to 30S by Thursday and the east along 25-30S passing by north of NZ on Friday.
Tasman Sea /NZ/Aus
Front travelling over NZ tonight followed by strong west to SW flow.
Deep Low down to 960hPa near 52S 175E on Monday night is expected to travel NE to east of Chatham Islands by Wednesday and then ease and go east. The following strong to gale SW flow should bring swells to over 6m to west coast by Tuesday and maybe to around 15m to Chatham Islands by early Wednesday. A brief ridge on Thursday, then another front and strong westerly change on Friday.
From Panama to Galapagos/Marquesas:
Mirror convergence zone is still there near5S from 110W to 150W, slowly shifting north.
ITCZ is mainly near 4N, and southerly winds are likely along 2N from 80W to 92w with a good tail current.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
No comments:
Post a Comment