# help interpreting a weather map

Hi, I need to know the answer for the following question, can anyone help providing one? Notice this is Southern Hemisphere, which affect wind direction etc.

I have no idea how the fronts move (the direction) and how fast they move, and how the wind directions changes.

Notice Wellington is on the southern tip of the North Island.
Question:

Describe the weather in New Zealand for the synoptic conditions shown below. Be systematic and focus on the spatial pattern of temperature and precipitation in each part of New Zealand including Wellington (where you should also estimate wind strength and direction). Comment on the weather to be expected in the 48 hours following the publication of this map. Note that the synoptic map is from the month of June.

Weather map below.

Why is your teacher assigning this as homework if it hasn’t been explained yet? Are you sure you were paying attention in class?

Sorry dude… we don’t answer homework questions here.

It’s not homework. It was a question in a previous final exam back in 2009. I just need to know the answer so I can know how to answer similiar question in the incoming exam if the lecturer decide to put in such question this year.

dead link. and btw i know the symbols on a weather map, what i need to know is specifics such as the wind direction, where the front gonna end up, how fast it moves etc.

Weather patterns move from west to east across NZ. There are no velocity indicators for the fronts so I don’t know how fast they’d be moving, but that front to the west would certainly be moving across the country in the next 48 hours. Wind is northwesterly ahead of the front and southwesterly behind it. Knowing the winds in wellington would require local knowledge that I don’t have. I do know that Wellington is a harbour town and the winds are strong as they get funnelled through the cook straight between the north and south islands. I’m not sure what else I can tell you. June is winter in NZ with temperatures between 0 and 20 degrees C for most of the country. Ahead of the front with the warmer northwester you might expect temps around 10 - 15 degrees and behind the front probably less than 10. Temps in the north of the country are higher than temps in the south of the country.

Don’t you have a text book that covers all this stuff?

There is a text book but it doesn’t help much with that question.

Do you know the reason why pre- cold front winds are west - northwest, and afterwards it becomes south- southwest? It doesn’t make any sense to me.

I can’t remember to be honest. I did aviation meteorology in NZ but it was a long time ago.

Winds generally circulate clockwise around low pressure areas (in the SH, counter-clockwise in the NH; high pressure areas are the reverse in each case); this is due to the Coriolis effect, due to Earth’s rotation (which also causes winds to be generally westerly in mid-latitudes, as part of a global circulation system). Fronts break up this pattern a bit; basically, the low pressure area isn’t symmetrical, usually you will see a “trough” of low pressure trailing from the low on the equatorial side, where the cold front is (on your map you can see that the isobars extend further out along the fronts). Also, wind direction can be read from the isobars (the lines with numbers on them, like 1000, 1005, etc, which shows sea level pressure); winds generally blow parallel to them (instead of directly from high to low pressure, again because of the Coriolis effect); isobar spacing also slows relative wind speeds (higher as they get closer/greater pressure differential).

IIRC, it’s because of the low-pressure system which is associated with the front.

Winds blow towards the center of a low, but spiral in a clockwise fashion due to the Coriolis effect (in the northern hemisphere, they spiral in a counter-clockwise fashion).

The net of this is that, as the front (and its attendant low) approach you, winds tend to be southerly. Once the front (and low) pass, you’re affected by the winds spiraling in to the backside of the low, which tend to be northerly.

Edit: ninjaed!

A gentle nudge in the right direction… Pressure Gradient.

Also that Low with 981mb is about 30 degrees to the West of Wellington, so it may be the major player 48 hours down the road.

Don’t forget to allow for this scenario being southern hemisphere.

I did, indeed, note this:

Yes, but you didn’t follow through. Winds ahead of a front in the southern hemisphere tend northerly and behind the front they tend southerly.

Ack, you’re right. My last sentence there was written from a northern-hemisphere POV.