How many millibars in how many hours?

[bilbobaggins]

[ QUOTE ]
gales are not always preceeded by a pressure change

[/ QUOTE ]

We agree, me an' thee - y'see.

But that would be in Lesson 2. And this thread started with a quessie about Lesson 1 - which our dear reader had forgotten.....

/forums/images/graemlins/wink.gif

 

[peterb]

You are quite right; it's the pressure gradient with distance that matters, not that with time. But at one station you can't measure the distance gradient, only the time gradient; fortunately that is usually a good guide to what's going to happen.

As a matter of interest I looked at the forecast chart last night; for 0600 this morning the forecast pressure difference between Anglesey and London was 16 millibars. I reckoned that to give a windspeed of about 75 knots (geostrophic) or about 50 knots at ground level. Not that far from what happened.

 

[belowdeckfan24]

Thank you. I Googled a question about Millibars per Hour and it brought me here. Now I understand why I just saw a video of a meteorologist getting choked up when he said that hurricane Milton had a drop of 50millibars in 10 hours. That's huge compared to the numbers mentioned here.

 

[Snowgoose-1]

That must have been a memorable lesson! /forums/images/graemlins/wink.gif

The RYA's excellent 'Weather Handbook' by Chris Tibbs suggests that a change of 5-6mb ( oh, all right, hectoPascales ) in 3 hours predicts a Force 6. A change of 8hPa in 3 hours is likely to foretell an F8, and one needs to consider *any* steep change in baro-pressure as a warning.

You'll find that helpful reminder at the back of the RYA's 'Course Notes' booklets.

Do not forget that a steep *rise* in pressure is also likely to presage a 'blow' - for it is the Pressure Gradient that initiates the change in wind velocity.

Does that help? /forums/images/graemlins/smile.gif

Very good. Thanks.
In a way, pressure watching has been somewhat pushed sideways with all the now available weather apps.

I have a Garmin wristwatch that continually monitors pressure . It beeps when the values set say so. I have found it really useful and accurate

 

[zoidberg]

I just saw a video of a meteorologist getting choked up when he said that hurricane Milton had a drop of 50millibars in 10 hours. That's huge compared to the numbers mentioned here.

'A blast from the past!'

It's not just meteorologists getting choked up re Hurricane Milton. Some are predicting that, if one possible track towards Florida's 'Big Bay' area happens, not only winds stronger than 150mph are likely but also storm surge of 23 feet!
Milton ‘explodes’ into Category 5 hurricane as Florida braces for 180-mph winds: Live

Some will 'poo-poo' dire warnings. No-one knows how bad this will get, where, for Florida's storm-battered people. To paraphrase the words of one local mayor 'When this thing hits, you'd better be somewhere else.'

 

[Martin_J]

This appears to be the video (courtesy of the BBC) of the meterologist that has just mentioned the drop of 50 millibars in 10 hours...
Meteorologist becomes emotional giving Hurricane Milton update

 

[zoidberg]

It seems the original tight eyewall has spawned another eyewall, further out, which causes a slight reduction in intensity of winds.... for a while. It is increasing in size/area, and is still 'hoovering' up heat-energy from the very hot waters of the Gulf as it wends its way towards Tampa. That suggests it could re-intensify back to a Grade 5 on the Saffir-Simpson scale. Some meteos are muttering about a 'Grade 6'.