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Tropical Thread


tombo82685

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Adam, any potential with that system that nam keeps developing off the caronlinas?

No, I don't think so. At least not as a tropical system. It looks baroclinic to me in the model progs (though it would have some moisture from the tropical wave north of the Greater Antilles).

baroclinic_instability has been hyping the Para NAM over on the main board, so I'm curious to see how this unfolds.

The Para NAM at 0z last night (07/05 00z) had a much weaker surface reflection than the op NAM at hr 84

(Note this is probably a time-sensitive link...you can access the Para NAM here: http://www.emc.ncep....ll/nampll_nmmb/ )

I spoke to dtk offline (he's the modeling guy from NCEP). He told me not to expect much better performance from the NAM in the tropics. All of the tuning they did to the model was to help across the US, not for the tropics.

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No, I don't think so. At least not as a tropical system. It looks baroclinic to me in the model progs (though it would have some moisture from the tropical wave north of the Greater Antilles).

I spoke to dtk offline (he's the modeling guy from NCEP). He told me not to expect much better performance from the NAM in the tropics. All of the tuning they did to the model was to help across the US, not for the tropics.

so is the para nam better than the regular nam across the US?

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so is the para nam better than the regular nam across the US?

I've not seen the error scores for it, but my assumption is that it will be. I don't do a lot of short range forecasting for the US, though, so I'm probably not the most qualified person to ask.

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The NAM wasn't intended for warm core systems correct?

Yeah, it overdoes convection. Don't quote me on it, but I think it has something to do with radiation balance/latent heat release. I think the mid-levels are too unstable and it causes deep moist convection too easily, which then causes precip bombs and too much vorticity, which feeds back on itself.

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Yeah, it overdoes convection. Don't quote me on it, but I think it has something to do with radiation balance/latent heat release. I think the mid-levels are too unstable and it causes deep moist convection too easily, which then causes precip bombs and too much vorticity, which feeds back on itself.

Yeah, it tends to overdo the low-level moisture as well many times which adds to the instability, setting off the convective triggers.

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Yeah, it tends to overdo the low-level moisture as well many times which adds to the instability, setting off the convective triggers.

I remember when people were saying that on dec 19th, 2009! Lol.

Thanks to you and Adam for answering.

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Since the tropical season is ramping up, I thought it would be a good time to take a look at some historic hurricanes in our region (immediate Philadelphia metro area). This discussion is focused on storms which have the most impact in Philadelphia. Other famous northeast hurricanes, such as 1938, 1944, 1960 Donna, and 1985 Gloria will not be discussed here because their impacts were relatively minor on Philadelphia compared to other nearby locations.

Disclaimer: I am not a met so I am sure I am missing quite a bit of nuance. I am hoping this post will serve as a starting point for a broader discussion. Much of my original interest in this topic was sparked by The Philadelphia Area Weather Book, written by Hurricane Schwartz and Jon Nese (this is an awesome book that I would highly recommend).

From what I can gather, it is the interaction of tropical and non-tropical features that seem to produce the most significant impacts in the Delaware Valley. While a Category 2 storm moving NW and making landfall on the Delmarva Peninsula would be catastrophic, that type of scenario hasn't happened in the last 200 years at a minimum. The last hurricane to make landfall in NJ or DE was a category 1 hurricane in 1903.

Instead, some cyclones manage to continue to generate strong winds long after they are purely tropical (e.g. 1878 Hurricane, 1954 Hazel). Other storms interact with mid-latitude troughs to produce prolific rains (e.g. 1999 Floyd).

Wind Producers

Two storms stand out in the historic record: the October 1878 Hurricane and Hazel 1954. In my research, these were the only 2 systems in the last 150 years that produced sustained hurricane force winds in the Philadelphia area. I believe the 94 mph gust recorded in Hazel is the highest on record in Philadelphia. Both were late season systems that made landfall in the Carolinas and then barrelled northward well inland while producing damaging winds over a wide swath of land.

Mets - what happened in both of these systems to allow hurricane force winds to be maintained well inland? It is because they were moving much faster than storms like Isabel 2003 and Fran 1996?

Other noted wind producers:

October 1846 (similar track to Hazel)

Chesapeake - Potomac Hurricane, August 1933

Isabel, September 2003 (gusts of 50 - 60 mph)

For more information:

The Hurricane of October 21-24, 1878, Delaware Geological Society

Hurricane Hazel (and other PA Hurricanes)

Rain Producers

Out of the top 10 highest recorded crests on the Schuylkill River at Philadelphia, 5 were attributable to tropical systems. The highest crest on record by more than 2 feet is attributable to the Saxby Gale of 1869. Not sure how much I trust the measurement given how long ago it was, but that is the crest of record.

Other tropical systems in the top 10:

Chesapeake - Potomac Hurricane 1933

Agnes 1972

Connie / Diane 1955

Floyd 1999

Both 1972 and 1955 were worse for the rest of PA than in Philadelphia but undoubtedly had some significant impacts in the city.

It's interesting that how the flooding occurred in these system is different. Agnes stalled over the region for days. Floyd interacted with mid-latitude features to produce copious amounts of rain on one day. The impact of Connie and Diane back to back within a week caused the major flooding.

Obviously, flash flooding is also a possibility with tropical systems, with Ivan and Jeanne in 2004 and Allison in 2001 being noted examples.

Storm Surge / Coastal Flooding

More to come in a future post.

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  • 4 weeks later...

We have Emily...modeling has it off of Florida by Friday...notsosure it's going to be a hurricane though given it's gotta trek over islands...and if it hits the DR or Haiti, it probably won't be a hurricane after Hispaniola is done with it.

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12z euro looks like it rams this right into the east coast of hati then off the west coast. It then just falls apart?

haiti is notorious for eating up weak systems like this due to it's mountain topography. I could see it being a possibility as the LLC hits resistance . But time will tell.

I think the models are all gonna have a tough time untill we figure out how well Emily holds up or breaks down.

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haiti is notorious for eating up weak systems like this due to it's mountain topography. I could see it being a possibility as the LLC hits resistance . But time will tell.

I think the models are all gonna have a tough time untill we figure out how well Emily holds up or breaks down.

yea i can see it doing that, i just haven't seen any models bring this east to west across hati. A lot of them have it cuting north to south across it bring it towards the bahamas.

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yea i can see it doing that, i just haven't seen any models bring this east to west across hati. A lot of them have it cuting north to south across it bring it towards the bahamas.

Im not sure if it's because some of the models are quicker to intensify her, hence, being bigger and getting pulled up by the trough. She;s been slow to organize, so i dont think you can go with any one model.

I saw the 18z GFS keeps her a bit west of Florida and winds her up. Basically, what im trying to say is, "i have no freaking clue!" haha.

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haiti is notorious for eating up weak systems like this due to it's mountain topography.

Actually, the island gets its Shredderola nickname because of what it does to well developed systems. Topography rips apart the well defined inner core of tropical cyclones. When there is no well defined inner core, it's not much different than going over any other land mass.

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