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Tropical Major Hurricane Irma (Part 1)

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Were very likely to have an upgrade to Hurricane Irma within the hour. You can see the eye currently developing this morning.
 
Webberweather53 said:
Yeah and the southeast coastline atm is still sitting somewhere in the middle of the clustering. For the sake of Texas and Louisiana let's hope Irma does not go over the Greater Antilles because if it does, the chances of a landfall there would go up dramatically...
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Asking for a friend cause he is an idiot wink wink. But are there statistics to that comment

Again asking for a friend
 
Looks like Hurricane Irma at 11:00 not to no one's surprise...

Hurricane IRMA
As of 12:00 UTC Aug 31, 2017:
Location: 16.7°N 33.4°W
Maximum Winds: 75 kt Gusts: N/A
Minimum Central Pressure: 987 mb
Environmental Pressure: 1012 mb
Radius of Circulation: 180 NM
Radius of Maximum Wind: 10 NM
Eye Diameter: N/A
 
I think everybody for the Bahamas to North Carolina better pay attention to this beast in the making
 
Webberweather53 said:
Typically this is the case because


In a nutshell yes, because the stronger system has a deeper rossby penetration depth (defined here by the height at which the circulation of the TC is very evident in the column, stronger TCs w/ larger circulations & generally taller/more persistent convection = deeper rossby penetration depth). This means that a stronger TC is also steered by a deeper layer of the troposphere and given that the winds become increasingly westerly with height as a tropical cyclone ventures away from the tropics this often implies faster recurvature for stronger storms. In addition, a stronger storm is liable to gain latitude for another reason: beta drift, which refers to a tropical cyclones' tendency to move in the absence of any steering! Beta drift/the beta effect usually accounts for about 10% of a tropical cyclone's motion and is estimated to add ~2-5 m/s to its translational speed and would be the net movement a TC would undergo if there was no net steering influence from a trough or ridge. Coriolis deflection increases w/ increasing latitude from the equator, as does the planetary vorticity (planetary vorticity is just the spin imparted on phenomena simply from earth's rotation). Effectively what occurs especially as a tropical cyclone becomes fairly intense, is that the differential in planetary vorticity advection across the storm increases and this leads to a net NW motion as a pair of beta gyres (w/ opposing signs) forms on opposite ends of the storm in the northern hemisphere this happens in the NW & SE quadrants. To understand how this works (as shown in the diagram below) and how we get an anticyclonic beta gyre and vis versa in the SE quadrant, we have to know that for example on the east side of the cyclone in the northern hemisphere, as air blows northward it gains planetary vorticity, as the impact of earth's spin becomes greater closer to the pole and thus, going back to the statement of the conservation of absolute vorticity (where absolute vorticity is the sum of planetary + relative vorticity) relative vorticity must decrease if planetary vorticity increases, thereby forming and an anticyclonic beta gyre in the NW quadrant of the storm. On the other hand, as northerly flow occurs on the western side of the hurricane, air moving southward loses planetary vorticity (f becomes smaller), thus in order to conserve absolute vorticity again, relative vorticity has to increase, thereby forming a cyclonic gyre. The net flow between these two beta gyres in the northern hemisphere is to the northwest and this flow which essentially accounts for the beta effect becomes more prominent for stronger hurricanes because their circulations are larger and stronger and thus there's a larger gradient in planetary vorticity (f) across them!
There are certainly other ways to understand the impact of the beta effect on tropical cyclone track but I think this way is much easier to digest but it still can be difficult (as it was for me) the first few times I learned/read about it.

This diagram below shows what I was talking about above, notice the pair of opposing beta gyres orientated from SW-NE across the tropical cyclone's circulation and that the flow between them is to the northwest. This essentially means that in the absence of any steering flow, a tropical cyclone in the northern hemisphere will tend to move to the northwest, with stronger/larger tropical cyclones having a greater tendency to do so vs smaller/weaker TCs.

Hope this helps!

View attachment 1000
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I appreciate the detailed response! Per usual great info web
 
So I'm curious can this early rapid intensification impact eventual track, ie: maybe spare US or does it not really matter with that honking atlantic ridge?
 
metwannabe said:
So I'm curious can this early rapid intensification impact eventual track, ie: maybe spare US or does it not really matter with that honking atlantic ridge?
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I thought Webb said something about the stronger the storm, the more north it would tend to go? But that is a beast ridge!
 
Tarheel1 said:
I thought Webb said something about the stronger the storm, the more north it would tend to go? But that is a beast ridge!
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Yeah generally that is the case but this seems to be a unique situation with the somewhat rare SW movement due to that ridge....
 
From NHC....
Given the strength of the ridge
and depth of the tropical cyclone, there are no obvious reasons to
discount the anomalous west-southwestward motion seen in most of the
guidance. Little change is made to the track forecast in short
range, but the track is shifted southward and westward at long
range, though not as far southwest as the overnight ECMWF and ECMWF
ensemble models.
 
145426_5day_cone_no_line_and_wind.png
 
Forecasted to become a cat 4 next week. Here we go again.

000
WTNT41 KNHC 311451
TCDAT1

Hurricane Irma Discussion Number 5
NWS National Hurricane Center Miami FL AL112017
1100 AM AST Thu Aug 31 2017

Satellite imagines indicate that Irma is rapidly intensifying.
Very deep convection has formed in the central dense overcast,
which is now displaying a small and clearing eye. Dvorak estimates
were up to 77 kt at 1200 UTC, and since the cloud pattern continues
to quickly become more organized, the initial wind speed is set to
85 kt.

Irma has moved somewhat south of and slower than all of the model
guidance since yesterday. Consequently, it stayed longer over the
warmer ocean temperatures away from the drier air to the north,
possibly allowing the rapid strengthening. Irma should move over
cooler waters tomorrow with some increase in mid-level dry air, so
hopefully the hurricane's intensity will level off by then. In a
few days, the hurricane will be moving over warmer waters with light
shear shown by all of the model guidance. This should promote
further strengthening of Irma, and the NHC forecast shows an
extremely dangerous category 4 hurricane next week, similar to the
solutions provided by the HWRF and the ECMWF models. The intensity
forecast is raised considerably from the previous one due to initial
trends, and is on the high end of the guidance at long range.

The hurricane has turned west-northwestward at about 9 kt. This
motion should continue for the next day or so before a ridge builds
over the central Atlantic Ocean. This ridge should force Irma to
turn westward by the weekend, and west-southwestward early next
week. Guidance continues to trend southward, following the trend of
the ECMWF model starting yesterday. Given the strength of the ridge
and depth of the tropical cyclone, there are no obvious reasons to
discount the anomalous west-southwestward motion seen in most of the
guidance. Little change is made to the track forecast in short
range, but the track is shifted southward and westward at long
range, though not as far southwest as the overnight ECMWF and ECMWF
ensemble models.
Like this
 
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