WEATHERGRAM
YOTREPS
Compiled Sun 3 September 2017
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.
Last month
Sea Surface temperature anomalies may be seen at www.ospo.noaa.gov/data/sst/anomaly/2017/anomnight.8.31.2017.gif
There continues to be more yellow than blue, more area covered by warm anomalies than by cool anomalies.
And there is still a warm river appearing along east coast of South America.
The eddies of cooler than normal water along the Eastern Equatorial Pacific looks like symptom of LA NINA, but the surrounding warmer than normal seas dilute this.
To see how the annual weather cycle and the seasons are working out, look at the average isobar maps from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html
In August, the subtropical ridge in the southern hemisphere lay in its normal seasonal latitudes between Fiji and NZ, with a disturbed westerly flow as far north as Bass strait to North Cape, somewhat further north than normal. Looking at the anomalies, we can see that wave 3 has been dominating proceedings, with HIGHS lingering in 3 places: South Atlantic and South Indian Oceans, and to SE of French Polynesia, and LOWS lingering in 3 places: over Chile, well south of South Africa, and over the Tasman Sea. Cyclonic northerly winds for NZ have been bringing a wet winter.
The wetter than normal conditions over northern NZ also show in the monthly rain map—but this map shows that peak anomaly has been to NE of NZ, and, when averaged over the whole month, is surprisingly near neutral over the NZ mainland.
Last 30 days of rainfall, and its anomaly, may be seen at trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.html
The monthly rain map shows heaviest rainfall along equatorial area from Indian Ocean to Indonesia, with some heavy rain over India, Nepal and Bangladesh, and a spot of heavy rain over Houston, Texas… (Three days of epic rainfall looks minor when averaged over a month). The anomaly map shows that the ITCZ is further north than normal--- this is a LA NINA trait, but it’s a real LOCAL La Nina.
TROPICS
Deluging rain from HARVEY brought damaging flooding to Houston.
The intensity of the rain in HARVEY was so much that NWS had to add a new colour to their rain map…
see www.youtube.com/watch?v=x28AcE5bxIo
And the intense monsoon continued in southeast Asia with a death toll of around 1,200 people, see www.theguardian.com/world/2017/aug/30/mumbai-paralysed-by-floods-as-india-and-region-hit-by-worst-monsoon-rains-in-years
This week, TC IRMA is in the Atlantic Ocean and model’s, at this stage, are suggesting that it might make landfall on North Carolina later this week.
And on the US west coast, TC LIDIA is expected to remain over the ocean put travel almost parallel to the coast.
And in the NW Pacific, remains of TC SANVU is fading as it approaches the Korean Peninsula, and a depression (MAWAR) is expected to make land fall to north of Hong Kong.
Last week’s rain map from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif shows enhancements in the rain over SE Asia, along the equatorial Indian Ocean, about the south of Japan (due to SANVU), over Eastern Pacific in the ITCZ, and a hotspot near Houston.
WEATHER ZONES
SPCZ=South Pacific Convergence zone.
This week, the SPCZ is expected to remain near Solomon Islands to Tuvalu and occasionally affect Tokelau.
A passing, mainly upper, trough, is expected to travel eastwards across Niue on local Sunday night and Southern Cooks on local Tuesday, preceded by NE winds, accompanied by variable winds and showers, and followed by SE winds.
Another passing trough may reach New Caledonia area around Saturday9 Sep local.
Subtropical ridge (STR)
HIGH over 1034hPa is travelling east along 40S for the next few days well south of French Polynesia, and as it moves away the winds over French Polynesia should weaken and turn easterly then Northeasterly.
Another HIGH, around 1022hPa, in northern Tasman Sea on Monday is expected to travel east along 25 to 30S this week across the South Pacific. it should help maintain moderate SE trade winds.
French Polynesia to the west:
The main obstacle this week is that travelling trough over Niue on local Sunday and Rarotonga on local Tuesday.
Departing northern NZ to the north or east for the tropics:
On Monday, a low travelling off to east of NZ should bring SW flow to the northern north Island.
On Tuesday, there should be a passing ridge with lighter winds.
On Wednesday, the forecast is for an increasing NW winds ahead of an approaching trough.
On Thursday and Friday, expect squally west to WSW winds, and rough seas.
By Saturday night, a Low around 1002hpa is expected to travel across northern N., followed on Sunday and Monday by showery SW/S winds.
SO maybe this isn’t the week to come or go, unless you can time departure on Tuesday or arrival on early Saturday.
If you would like more detail for your voyage, then check metbob.com to see what I offer.
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See my website http://www.metbob.com for more information
Feedback to bob@metbob.com or txt 6427 7762212
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
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