Bridget Beddow
I'm still weather illiterate here.
What do you mean by no convection advecting those winds to the surface?
8/03/04 FCST|Gulf|Hurricane Alex
- Thread starter Chris Sokol
- Start date
I'm still weather illiterate here.
What do you mean by no convection advecting those winds to the surface?
Zach Bailey
EF2
Let me take a stab at this one: advection is "The horizontal transfer of air mass properties by the velocity field of the atmosphere." Now, what you need is some sort of convection to transfer these air mass properties (i.e. the wind speed, vorticity, etc.) along the ground so that they can be felt. If you're in a hurricane and there's no convection around to transfer the air mass properties (pressure changes leading to strong wind) then you're not going to feel nearly as much wind as in the convection. Hence why the winds in the eyewall are the strongest (lots of convection there moving very quickly to move the air mass), but yet in the eye (where there's no convection) you have no wind.
B Ozanne
EF5
For reasons I wont go into do you accept that it is windier the higher up you go? Ok, and as you get towards the surface friction slows the wind. If you get a thunderstorm the windy air up high will be brought to the surface before friction slows it down. That is also why you get gusts, windier air from aloft is brought to the surface. During hurricanes the highest winds are recorded during the rain squalls. The rain and other vertical movements are "advecting" higher winds aloft to the surface.
Bridget Beddow
B Ozanne wrote:
Okay, I gotcha now.
Thank you, also, Zach
Chris Rozoff wrote:
Thank you, too, Chris.
Maybe one of these days, I'll be able to understand enough to be able to give a better description of my hurricane experiences :study:
Okay, I gotcha now.
Thank you, also, Zach
Chris Rozoff wrote:
Thank you, too, Chris.
Maybe one of these days, I'll be able to understand enough to be able to give a better description of my hurricane experiences :study:
B Ozanne
EF5
I agree, as you get very high up in a hurricane the winds decrease, but 850-700mb probably have the strongest winds and getting those to the ground is what I am talking about.
Zach Bailey
EF2
Indeed. Very symmetric, text-book appearance with good outflow. I would agree with you that it appears stronger than when it was glancing the NC coast since to me it appears the eye has contracted a little and has cleared out and according to the IF sat pics, there is an intact eyewall.
However it appears to have come too late as Alex will soon be over less than 26C waters which will mean it loses the tropical moisture to feed off of and will become a cold-core system. Perhaps it will give the brits a good thrashing when it makes it across the pond (check out the extended forcast, days 4 and 5 have it making a beeline for the UK).
Geoff Boyle
Do you guys think it will have any strength to bother the UK?
I thought once it hit cold water then it would loose most it's strength within 48 hours.
I thought once it hit cold water then it would loose most it's strength within 48 hours.
B Ozanne
EF5
Hurricanes make it to the UK all the time as extra-tropical storms. Just your average rain/wind event.
NJ had some amazing swells this mornings. Overhead sets with offshore winds. Tomorrow looks good too with more offshore winds and hopefully more swells coming off Alex.
NJ had some amazing swells this mornings. Overhead sets with offshore winds. Tomorrow looks good too with more offshore winds and hopefully more swells coming off Alex.
Glen Romine
EF5
Better to say that a hurricane is a heat engine, and a relatively inefficient one at that. The sun warms the ocean surface, and evaporates water, that water vapor having latent heat that is later released as condensed clouds, and these clouds radiate energy back out to space, completing the engine cycle. I think using the term convective forcing is mis-leading - because when you say convection most people think of overturning in the atmosphere - but stratiform rain within a hurricane is much more widespread and likely a larger contributor to the overall heat budget.
That heat energy is maximized at ~ 700 mb in the typical hurricane, but heating occurs throughout the cloud-bearing layer where there is ascent occuring. Peak rotational winds will occur closer to top of the boundary layer height - and decreasing gradually with increasing height, as you mentioned because of the thermal wind relationship for a warm core system, the horizontal pressure gradient, which is what really drives the winds, is much greater near the surface than aloft. As mentioned, surface friction acts to slow the winds within ~ 500 m of the surface owing to turbulent eddies.
See http://www.nhc.noaa.gov/gifs/JLF_Fig1.gif
Actually, I think there is some clear evidence for convective enhancement of the downward momentum transport - a.k.a. strong gusty winds at the surface accompanying squalls. The precipitation drag aids in the enhancing downdrafts, which are interspersed among bands of ascent. So there is some truth to the notion that active local convection can increase the likelihood of the higher winds at the top of the boundary layer making it to the surface without mixing out towards the mean wind profile.
By PV, do you mean potential vorticity? That's probably a bit elevated a subject for here, but since convection causes latent heat release, and the thermal perturbations are a form of potential vorticity anamoly, then you get into a bit of a chicken or the egg argument. Horizontal winds are potentially variant within rainbands, but could be owing to variations in vertical momentum transport, etc... but I don't think PV bands could easily be tied to specific surface wind gusts. The scales are too far separated IMO. Instead, PV bands can enhance the probability of local convective development in the form of squalls/bands, and convective winds wthin this individual convective elements can enhance vertical momentum transport.
Ok, this got really long - sorry - this whole conversation really belongs in weather and forecasting - not the Target thread - but I don't have the authority to move it. Maybe a moderator could step in and do so.
Glen
Zach Bailey
EF2
To bring the forecast thread back on track, let me just add that the latest discussion increased the winds to 90kt and has the system staying AOB hurricane strength for a good stretch across the atlantic. It will be interesting to see if this has any effect on the British Isles.
Get it here:
http://www.nhc.noaa.gov/text/refresh/MIATC...ml/042037.shtml?
Get it here:
http://www.nhc.noaa.gov/text/refresh/MIATC...ml/042037.shtml?
Zach Bailey
EF2
Alex has now entered the record books as the strongest storm to form as far north as it did (above 38N latitude).
Alex continues to amaze with its strength and organization. Wind speeds have been increased to an amazing 105kt with the latest advisory and alex still maintains an impressive structure on satellite views.
The storm is still expected to transition to an extratropical system by 48 hours.
Get the latest here: http://www.nhc.noaa.gov/text/refresh/MIATC...ml/050256.shtml?
Alex continues to amaze with its strength and organization. Wind speeds have been increased to an amazing 105kt with the latest advisory and alex still maintains an impressive structure on satellite views.
The storm is still expected to transition to an extratropical system by 48 hours.
Get the latest here: http://www.nhc.noaa.gov/text/refresh/MIATC...ml/050256.shtml?
mark humpage
EF2
I'll keep you posted :wink:
We await in anticipation.
Mark
B Ozanne
EF5
Has the NHC correctly forecasted the wind speeds of this system once?
This should be a real eye opener (no pun intended) on how easily this strong CAT III system could have hit the Northeast US. EVerybody knows strong storms have hit New England in the past but nobody thinks it could happen again. It's just a matter of time when everything comes together and a major hurricane hits New York. I call it the $100 billion storm...and its coming.
On another note storm relative winds are 120 mph with a forward speed of 30mph. That gives max sustained winds of 150mph...nearly a CAT V.
This should be a real eye opener (no pun intended) on how easily this strong CAT III system could have hit the Northeast US. EVerybody knows strong storms have hit New England in the past but nobody thinks it could happen again. It's just a matter of time when everything comes together and a major hurricane hits New York. I call it the $100 billion storm...and its coming.
On another note storm relative winds are 120 mph with a forward speed of 30mph. That gives max sustained winds of 150mph...nearly a CAT V.
Bridget Beddow
Chris Rozoff wrote:
Alot of people around this area and along the coastline seem to tune in more to a hurricane/ts once it hits the gulf stream, due to how it seems to affect most storms that cross its path.
It's so amazing how much of an affect the gulf stream has on the way of life. That is the primary spot for fishermen on tournaments as well for the Big Rock Tournament- due to the change in water temperatures. And it has always amazed me how something that seems so small (width-wise) can have such a dramatic affect on something so large as a hurricane.
Alot of people around this area and along the coastline seem to tune in more to a hurricane/ts once it hits the gulf stream, due to how it seems to affect most storms that cross its path.
It's so amazing how much of an affect the gulf stream has on the way of life. That is the primary spot for fishermen on tournaments as well for the Big Rock Tournament- due to the change in water temperatures. And it has always amazed me how something that seems so small (width-wise) can have such a dramatic affect on something so large as a hurricane.
rdale
EF5
"On another note storm relative winds are 120 mph with a forward speed of 30mph. That gives max sustained winds of 150mph"
NHC's latest says max sustained winds are 120mph - where did you see the 150 report? Are you thinking that NHC doesn't incorporate motion into their wind reports?
- Rob
NHC's latest says max sustained winds are 120mph - where did you see the 150 report? Are you thinking that NHC doesn't incorporate motion into their wind reports?
- Rob
