Well when a mommy storm and a daddy storm love each other very much...
OT: Official Hurricane Irma Thread
- Thread starter RU4Real
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Well when a mommy storm and a daddy storm love each other very much...
Okay, folks, let's settle down. 
Storm surge. It's a pretty easy concept in principle - the winds from a storm push water in front of it. When the water gets to land, it piles up. Think of the ocean as snow in your driveway and the storm as you pushing a snow shovel.
There are, however, a number of factors that contribute to how high a surge is:
1. Wind speed - the faster the wind, the more water it can move
2. "Fetch" - an old nautical term adopted by meteorology, 'fetch' is the distance that the wind blows, unobstructed. It's why storms are so bad - and seas are so massive - in the Southern Ocean. At the latitudes between Cape Horn and Antarctica there is no land, so the wind just circles the globe, unobstructed.
3. Wave height - a storm pushes a mass of water in front of it, but there are also, as you might expect, waves on top of that water. You may recall from our encounter with Sandy, when we spoke of the surge height and the wave height as two different things
3. Shore topology - this is a really big factor. Waves can only get so high - an easy rule of thumb is 80% of the water's depth - before they break. So you can have HUGE waves in a major storm at sea but closer to shore those waves will break and so won't contribute that much to the surge height. Conversely, a shallow coast will cause a surge to build higher as the water basically runs out of basin depth approaching the shoreline. This is why we often see an inverse relationship between surge height and wave height in different locations based on shoreline topology.
With hurricanes we consider storm surge from the same perspective as wind speed. A hurricane's strongest winds are on the right-hand side of the storm, relative to its forward motion. Those winds push water in front of the storm, while the winds on the left side of the storm, blowing in the opposite direction, tend to push water away from it. Because the storm's relative motion is part of the wind speed math, we see bigger surge in the right quadrants than in the left quadrants because of the wind speed differential.
So the Bahamas, in this case, are in dire trouble because they will be on the right side of the storm at the end of a very long fetch. There will be a LOT of water piled up in front of Irma when she approaches the Bahamas so the surge will be very severe. On the other side of the storm, where the coast of Florida lies, there will be a long fetch from the right quadrants as the storm approaches but once it turns northward the Florida coastline will be on the left side and the surge effect will be somewhat mitigated. In fact, once the eye of Irma passes any given point on the Florida coast, the wind will begin to actually blow the ocean water out to sea, as opposed to onto the beach.
Ergo, I personally think that the 20 - 25 foot surge numbers being tossed around for southern Florida are overdone. Depending on when Irma begins her northward motion, my expectation for surge in the Miami area is more like 12 - 15 feet.
Storm surge. It's a pretty easy concept in principle - the winds from a storm push water in front of it. When the water gets to land, it piles up. Think of the ocean as snow in your driveway and the storm as you pushing a snow shovel.
There are, however, a number of factors that contribute to how high a surge is:
1. Wind speed - the faster the wind, the more water it can move
2. "Fetch" - an old nautical term adopted by meteorology, 'fetch' is the distance that the wind blows, unobstructed. It's why storms are so bad - and seas are so massive - in the Southern Ocean. At the latitudes between Cape Horn and Antarctica there is no land, so the wind just circles the globe, unobstructed.
3. Wave height - a storm pushes a mass of water in front of it, but there are also, as you might expect, waves on top of that water. You may recall from our encounter with Sandy, when we spoke of the surge height and the wave height as two different things
3. Shore topology - this is a really big factor. Waves can only get so high - an easy rule of thumb is 80% of the water's depth - before they break. So you can have HUGE waves in a major storm at sea but closer to shore those waves will break and so won't contribute that much to the surge height. Conversely, a shallow coast will cause a surge to build higher as the water basically runs out of basin depth approaching the shoreline. This is why we often see an inverse relationship between surge height and wave height in different locations based on shoreline topology.
With hurricanes we consider storm surge from the same perspective as wind speed. A hurricane's strongest winds are on the right-hand side of the storm, relative to its forward motion. Those winds push water in front of the storm, while the winds on the left side of the storm, blowing in the opposite direction, tend to push water away from it. Because the storm's relative motion is part of the wind speed math, we see bigger surge in the right quadrants than in the left quadrants because of the wind speed differential.
So the Bahamas, in this case, are in dire trouble because they will be on the right side of the storm at the end of a very long fetch. There will be a LOT of water piled up in front of Irma when she approaches the Bahamas so the surge will be very severe. On the other side of the storm, where the coast of Florida lies, there will be a long fetch from the right quadrants as the storm approaches but once it turns northward the Florida coastline will be on the left side and the surge effect will be somewhat mitigated. In fact, once the eye of Irma passes any given point on the Florida coast, the wind will begin to actually blow the ocean water out to sea, as opposed to onto the beach.
Ergo, I personally think that the 20 - 25 foot surge numbers being tossed around for southern Florida are overdone. Depending on when Irma begins her northward motion, my expectation for surge in the Miami area is more like 12 - 15 feet.
In that case, is the storm surge for the second landfall in SC (given the storm will have completed its turn 1-2 days before and be pushing a lot of water directly at the SC coast) something that isn't really talked about right now that may turn into a big problem?Okay, folks, let's settle down.
Storm surge. It's a pretty easy concept in principle - the winds from a storm push water in front of it. When the water gets to land, it piles up. Think of the ocean as snow in your driveway and the storm as you pushing a snow shovel.
There are, however, a number of factors that contribute to how high a surge is:
1. Wind speed - the faster the wind, the more water it can move
2. "Fetch" - an old nautical term adopted by meteorology, 'fetch' is the distance that the wind blows, unobstructed. It's why storms are so bad - and seas are so massive - in the Southern Ocean. At the latitudes between Cape Horn and Antarctica there is no land, so the wind just circles the globe, unobstructed.
3. Wave height - a storm pushes a mass of water in front of it, but there are also, as you might expect, waves on top of that water. You may recall from our encounter with Sandy, when we spoke of the surge height and the wave height as two different things
3. Shore topology - this is a really big factor. Waves can only get so high - an easy rule of thumb is 80% of the water's depth - before they break. So you can have HUGE waves in a major storm at sea but closer to shore those waves will break and so won't contribute that much to the surge height. Conversely, a shallow coast will cause a surge to build higher as the water basically runs out of basin depth approaching the shoreline. This is why we often see an inverse relationship between surge height and wave height in different locations based on shoreline topology.
With hurricanes we consider storm surge from the same perspective as wind speed. A hurricane's strongest winds are on the right-hand side of the storm, relative to its forward motion. Those winds push water in front of the storm, while the winds on the left side of the storm, blowing in the opposite direction, tend to push water away from it. Because the storm's relative motion is part of the wind speed math, we see bigger surge in the right quadrants than in the left quadrants because of the wind speed differential.
So the Bahamas, in this case, are in dire trouble because they will be on the right side of the storm at the end of a very long fetch. There will be a LOT of water piled up in front of Irma when she approaches the Bahamas so the surge will be very severe. On the other side of the storm, where the coast of Florida lies, there will be a long fetch from the right quadrants as the storm approaches but once it turns northward the Florida coastline will be on the left side and the surge effect will be somewhat mitigated. In fact, once the eye of Irma passes any given point on the Florida coast, the wind will begin to actually blow the ocean water out to sea, as opposed to onto the beach.
Ergo, I personally think that the 20 - 25 foot surge numbers being tossed around for southern Florida are overdone. Depending on when Irma begins her northward motion, my expectation for surge in the Miami area is more like 12 - 15 feet.
TWC earlier this morning made mention of this, though in relation to the low lieing area's of coastal Ga. And if Florida is spared by this thing tracking a little east, I imagine Ga and SC will then take it pretty hard. Similar to Mathew last year, but this one is bigger and stronger.
The models are suggesting a Cat 1 storm at landfall in SC. I don't know much about the shoreline down there, but I wouldn't expect much more than 8 - 10 feet of surge with a Cat 1. There's good fetch over open ocean, but the angle of Irma's approach, if you can visualize that, will cut the duration a bit.
That happened up here with Gloria here in 1985. I lived in Ship Bottom at the time. An insane confluence of events happened to make what could have been utter destruction into a mere nuisance. It had been a cat 5 heading straight toward us. It weakened to a three, moved 30 - 5- miles east and sped up hitting us at dead low tide. It came up to my door (which I only know because of the bay debris on the porch but did not get in the house. Three days of cleaning the yard of some pretty bad glop and we were good as new.
For reasons unknown my electric mower, which had to have been submerged, not only still worked but continued to for several years.
Wikipedia-
Tropical cyclones typically form over large bodies of relatively warm water. They derive their energy through the evaporation of water from the ocean surface, which ultimately recondenses into clouds and rain when moist air rises and cools to saturation. This energy source differs from that of mid-latitude cyclonic storms, such as nor'easters and European windstorms, which are fueled primarily by horizontal temperature contrasts
Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides suitable conditions for many types of ecosystems, as well as water for hydroelectric power plants and crop irrigation.
The major cause of rain production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts. If enough moisture and upward motion is present, precipitation falls from convective clouds (those with strong upward vertical motion) such as cumulonimbus (thunder clouds) which can organize into narrow rainbands. .
This is Barbuda in the eye of Irma's 185 mph winds this morning. This pic captures so well the duality of the astonishing beauty and terrible reality of extreme storms like this.
So what's it like to be IN the eye for that time. Is it...calm?
In Puerto Rico, phone lines are down and over a million people are without power.
Which is crazy when there are just 3.5 million people there.
The winds don't appear to have cause any major damage like the other islands at least. But no one knows when the power will be restored, could be days, weeks, or months.
Which is crazy when there are just 3.5 million people there.
The winds don't appear to have cause any major damage like the other islands at least. But no one knows when the power will be restored, could be days, weeks, or months.
I was living on the College Ave campus at the time and remember the hype, playing of any rock song named Gloria on the radio, everyone taping up their dorm windows. Then it skirted us (in NB). IIRC, we has a football game at Giants Stadium after the storm passed that was still on (Penn State or BC, forgot which one though). I recall that it didn't hit NB as bad as predicted.
She's also willing to risk it all based on familiarity with other people. May God be with her.
My parents in Naples are doing the same. Not what I would do, but I'm not them.
Gloria was never a Cat 5. For a while it was the strongest Cat 4 to never make Cat 5, but it lost that honor to another storm, the name of which escapes me at the moment.
It was a Cat 4 approaching the Bahamas, decaying to a Cat 2, then Cat 1 before briefly restrengthening to Cat 2 status off the Delmarva.
Gloria was a great example of media hype run amok. It had a huge wind field and precip shield and in some places dumped a good amount of rain but ultimately the effects fell well short of anything that was advertised.
CNN Headline. IRAN? We are so screwed.
Hurricane watches issued for parts of Florida as Iran roars toward US
Hurricane watches issued for parts of Florida as Iran roars toward US
Only have a few minutes today and haven't read much since this morning, so my apologies if all of this has been covered by others and this is a repeat.
Anyway, below is the updated 11 am track, which is just about identical to the 5 am track. Zeroing in on a SE Florida landfall, basically in Miami. Obviously the "Cone of Uncertainty" is much wider still, but the center of the track, i.e., the most likely landfall, is SE Florida, with the storm then projected to scrape up the FL east coast all the way to just off the coast of Jacksonville, then landfalling again near Savannah, then going well inland. A Gulf coast landfall is becoming unlikely as is a path completely out to sea. Looking like something between coming right up the center of FL to coming up 30-50 miles offshore of FL (but then still hitting GA/SC) is likely with the Miami/east coast of FL solution being most likely. At this time.
Projected winds are in the 150 mph range at landfall near Miami, dropping to ~120 mph near Jacksonville and then Savannah. Storm surges in South Florida from Miami to West Palm Beach would be in the 7-10' range for a strong cat 4 (vs. 15-20' in the Bahamas due to a host of factors), as per Jeff Masters; see the link. Surges would be greater further north for a Cat 4, but hopefully Irma will weaken some before then.
Make no mistake about it - a landfall in South Florida of a near Cat 5 (or strong Cat 4) hurricane will be historically catastrophic, since the last landfalling Cat 5 was Andrew, which was small and missed Miami to the south and the other Cat 5 was the Labor Day storm in 1935 that hit the Keys from SE to NW, missing the peninsula. With all the people and buildings now in its path, the devastation in areas within 20-30 miles of where the eye travels (i.e., within the eyewall) could be beyond anything seen in the US before.
https://www.wunderground.com/cat6/hurricane-irma-extreme-storm-surge-threat-us-and-bahamas
Anyway, below is the updated 11 am track, which is just about identical to the 5 am track. Zeroing in on a SE Florida landfall, basically in Miami. Obviously the "Cone of Uncertainty" is much wider still, but the center of the track, i.e., the most likely landfall, is SE Florida, with the storm then projected to scrape up the FL east coast all the way to just off the coast of Jacksonville, then landfalling again near Savannah, then going well inland. A Gulf coast landfall is becoming unlikely as is a path completely out to sea. Looking like something between coming right up the center of FL to coming up 30-50 miles offshore of FL (but then still hitting GA/SC) is likely with the Miami/east coast of FL solution being most likely. At this time.
Projected winds are in the 150 mph range at landfall near Miami, dropping to ~120 mph near Jacksonville and then Savannah. Storm surges in South Florida from Miami to West Palm Beach would be in the 7-10' range for a strong cat 4 (vs. 15-20' in the Bahamas due to a host of factors), as per Jeff Masters; see the link. Surges would be greater further north for a Cat 4, but hopefully Irma will weaken some before then.
Make no mistake about it - a landfall in South Florida of a near Cat 5 (or strong Cat 4) hurricane will be historically catastrophic, since the last landfalling Cat 5 was Andrew, which was small and missed Miami to the south and the other Cat 5 was the Labor Day storm in 1935 that hit the Keys from SE to NW, missing the peninsula. With all the people and buildings now in its path, the devastation in areas within 20-30 miles of where the eye travels (i.e., within the eyewall) could be beyond anything seen in the US before.
https://www.wunderground.com/cat6/hurricane-irma-extreme-storm-surge-threat-us-and-bahamas
I got stuck in Palm Beach in 2005 for Hurricane Jeanne which was a Cat2/3, and hit at night. The only way I can describe the noise of the wind is to compare it to laying on a runway at Newark with jet after jet flying low over your head. It is terrifying.
89 mph appeared to be the highest winds. It was not so much the wind, but the tidal surge.
Right thanks. I was just curious. I was inland and we tons of downed trees/power lines so just wanted to compare.
4Real - skimmed through the thread. Great posts on surge and stuff. Just want to make one correction. The latest NHC discussion still has Irma at Cat 3, off of Jacksonville at 120 mph and over the open water, so I wouldn't expect too much weakening between there and Savannah/Hilton Head, about 100 miles away, i.e., Irma will still likely be a strong Cat 2/weak Cat 3 and could have a surge of 10-15' (or more if mid Cat 3), as per Jeff Masters' post yesterday.
https://www.wunderground.com/cat6/hurricane-irma-extreme-storm-surge-threat-us-and-bahamas
The low country landfall is going to be really interesting because their experience will fluctuate with Irma's track through Florida just as much as that of the folks in coastal Florida.
A heavy contact encounter with Florida makes Irma a Cat 1 in southern SC. A track more like the 12z GFS, or a tick east of that, even, means she could easily be a 3 or possibly a 4 when she gets to the low country.
Uh oh - new Euro, the best model with this storm, so far and historically, makes landfall midway between Naples and Miami at the bottom of the peninsula. Gottal run, but this might be better for Miami, but is pretty bad for the rest of South Florida and towad the Gulf. This is why evacuation planning is so hard - a tiny shift in when Irma turns north makes a huge shift in what part of Florida Irma hits.
The 12z Euro is running a horror show for southern Florida right now. Guidance to 72 hours puts the eyewall right over the keys, then it comes back a bit east of north and puts Miami in the RFQ (right front quadrant). Worst case scenario for the Keys and Dade County. The track from that point is up the spine of the peninsula.
The good news with this run is that Irma only makes it as far as Jacksonville before it transitions to extra-tropical and drifts off to the NNW, dissipating in the Tennessee valley.
The good news with this run is that Irma only makes it as far as Jacksonville before it transitions to extra-tropical and drifts off to the NNW, dissipating in the Tennessee valley.
It's getting pretty close to being that way, yes. There's amazing model consensus and consistency with this storm. If the predictions are accurate then they are definitely screwed.
I know what you mean, but Donna traversed much more land than Irma would on the NHC track and entered as a Cat 4 at Naples, but still exited as a Cat 2 south of Jacksonville. Doesn't guarantee that happens with Irma, but Cat 2/3 is quite possible with the NHC track and, as you noted, if it stays offshore completely Cat 4 is quite possible.
https://en.wikipedia.org/wiki/Hurricane_Donna
Wonder how the Seven Mile Bridge will fare.
Do the Fire, EMS and other agencies abandon the Keys? That's what the 43rd did during Sandy (at least the FD).
Poor Homestead. Looks like they'll get wiped off the map just like 25 years ago.
I don't know for certain but I think they would at least consolidate some of their assets. Some of those islands will absolutely go under water, others are a little higher. Interesting question.