Written by Dr David Fountain, Associate Professor Plant Biology (Retired), Institute of Molecular BioSciences, Massey University
Summer is the time of year when there’s lots of pollen – and hayfever – around.
Pollen grains are shed from flowering plants and are typically 15 to 50 millionths of a metre across – about the same width as a human hair.
From multiple source plants such as a pine plantation or fields of flowering grass, pollen may be produced as a mass blanket of particles in the air. Pine pollen in New Zealand can often be seen as yellow clouds over trees and as yellow drifts or scum on water.
Production of pollen depends on (among other things) the time of year and time of day, temperature, vegetation type and altitude – and clearly, these factors are not all independent of each other.
Wind direction and weather affect local pollen concentration: the wind moves it about, and rainfall washes it out of the air. Pollen grains stream out in the air-flow just like a smoke plume and can be carried long distances.
For example, in Scandinavia birch pollen allergy and asthma symptoms appear long before birch trees flower there. The pollen arrives from as far south as Italy, where flowering occurs much earlier.
In New Zealand, the pollen forecast for today and tomorrow is available for selected towns and cities. The forecast of ‘low’, ‘moderate’ or ‘high’ is based on an assessment of the factors influencing pollen production, concentration and movement. Pollen type is also mentioned in the forecast because this influences the “strength” of the allergy.
All MetService inshore recreational marine forecast areas are now covered by a full warning service. This extension of services started on Tuesday 7 December 2010.
Previously, a full suite of wind warnings only applied to the four Auckland recreational marine areas (Manukau Harbour, Waitemata Harbour, the Hauraki Gulf and for the area from Bream Head to Cape Colville) with STORM at the high end of the continuum, GALE and SQUALL in between, and STRONG WIND (now known as a ‘Strong wind advisory’) at the lower end. In the other eight inshore recreational marine areas – Bay of Islands, Coromandel, Bay of Plenty, Hawke Bay, Kapiti, Mana, Wellington and Christchurch- only GALE or STORM warnings were referenced for the adjacent Coastal areas. In the new format, each inshore area receives a separate warning as appropriate.
Here is a full definition of the new warning scheme
STORM warning is issued whenever the average wind speed* is expected to exceed 47 knots.
GALE warning is issued whenever the average wind speed* is expected to exceed 33 knots but not 47 knots.
SQUALL warning is issued whenever a gale or storm warning is not in force, and the sudden onset of strong winds is expected to produce squalls with wind speeds of 35 knots or more lasting up to one hour. In addition, squalls should exceed the average wind speed* by 15 knots or more.
STRONG wind advisory is issued whenever the average wind speed* is expected to reach 25 knots and remain less than 34 knots.
The SQUALL warning is particularly useful for warning mariners of intense, short-lived weather events that are associated with gale or storm force winds. They are most likely to be issued during a period of severe thunderstorm activity and/or with the passage of an active cold front. When a squall warning is issued, the following statement is added to the forecast: “Waves may rise rapidly during squalls”
For the eight non-Auckland inshore recreational marine areas, when a warning or advisory applies its status will be mentioned at the beginning of the forecast, immediately after the naming of the area and before the details of the forecast. At the start of these forecasts reference is given of the warning status of adjacent Coastal areas. This new service does not apply to the Lake Taupo or Lake Rotorua forecasts.
*Notes on “average” wind speed:
Winds mentioned in MetService marine forecasts are average winds that have been chosen to represent likely conditions in a nominated area for a nominated period. An average wind is considered to be a wind averaged over a ten minute period at a reference level of 10 metres above sea level. Average wind speeds are given in increments of 5 knots and directions are given to the nearest octant (i.e., north, northeast, etc.) FROM which the wind is coming, in degrees true.
Momentary gusts, lasting a few seconds, may add as much as around 50% to the average wind speed. Prolonged squalls, possibly lasting up to an hour, may result in brief gales and add 15 knots or more to the average wind speed.
Significant wind changes are mentioned. In COASTAL forecasts a significant change is 10 knots and/or 90 degrees. INSHORE areas are more detailed and changes in average wind of 5 knots and/or 45 degrees can be mentioned.
Marine Weather Situation and Forecast issued at… by MetService
NIL warning for PLENTY
A slow moving low just west of the North Island gradually weakens over the next few days and is then expected to cross the North Island on Tuesday.
Forecast issued at…
Valid to midnight Sunday for Inshore waters from Matakana Island to Mayor Island to Motiti Island and then east to Torere River mouth.
Waves may rise rapidly during squalls
Northerly 15 knots rising to 25 knots this afternoon, with gusts 35 knots and possibly reaching 60 knots in squalls.
Sea becoming rough this afternoon.
Poor visibility in heavy showers and squally thunderstorms.
(C) Copyright Meteorological Service of New Zealand Ltd 2010
For the four Auckland recreational areas the only change is that the words “WIND WARNING” have been replaced by “STRONG WIND ADVISORY”. These four areas are combined when appropriate, or split when necessary, so at the start of this forecast a combined warning status message for these four areas is given. These areas are also covered by a brief separate status message, called a VHF warning, which is given a sequence number that is reset to A01 at the start of each month.
FOR VHF BROADCAST: Issued XXXX NZDT XXXday DD-MMM-YYYY
Valid until 2359 NZDT (next day) DD-MMM-YYYY
STRONG WIND ADVISORYA27 FOR THE MANUKAU AND WAITEMATA HARBOURS, THE HAURAKI GULF AND THE AREA FROM BREAM HEAD TO CAPE COLVILLE:
Becoming southwest 25 knots gusting 35 knots around midday today, then easing below warning criteria this afternoon. Rising to northwest 25 knots gusting 35 knots Tuesday night.
This warning cancels and replaces WARNING A26
(C) Copyright Meteorological Service of New Zealand Ltd YYYY
Auckland recreational marine Forecast issued at … by MetService
Strong wind advisory is in force for all areas.
A trough over the North Island moves away to the east today, allowing a ridge to move onto the country. However, this should be swiftly followed by another trough, sweeping over the region late Tuesday, bringing strong disturbed southwesterlies.
Forecast issued at XXXX XXXday DD-MMM-YYY
Valid to midnight (next)day:
These changes are intended to help mariners in our inshore waters appreciate the likely impact of wind speed transitions from lower values, through the advisory of strong winds, to the warning status of squall, gale or storm. Squall warnings will be able to extend the information contained in any Severe Thunderstorm Warning from land areas to adjacent inshore marine areas. We want boaties to realise that when they hear the word “warning” they take time to check it out: it may only apply to part of the area for part of the time, and IMMEDIATEACTION may be required to avoid its peak.
All coastal and recreational area weather forecasts are now available on a special website for mobile cell phones, http://m.metservice.com.
MetService wishes you safe boating and plenty of enjoyable weather this summer.