Atlantic - Laura forms August 21, 2020 (rainfall, days, storms, meteorology)

[Psychoma]

Fri 21Aug 9aEDT/AST Tropical Storm Laura forms (formally 98L & TD13) after air recon investigates flare up of storms just as sun came up that's been holding together so far.

Winds 45mph(75km/h), moving W 21mph(33km/h), pressure 1008mb
Located about 230miles(375km) ESE of N Leeward Islands.
NHC will update cone map with the 11aEDT update, but likely keeps a more southern route which would keep storm weaker being closer to higher terrain next few days. This may mean storm peaks in the Gulf versus before FL but details still TBD.

Interaction with TD14 in the Gulf will be interesting. Storms don't like being near each other, one will usually weaken the other, or they both hinder each other vs if left to themselves, or they spin around each other (Fujiwhara effect). And I see this asked a lot, but no, storms don’t combine to become a monster storm. For an explainer see Jack's post here, but remember details are still unknown at this point:
https://twitter.com/jacksillin/statu...99327806009344

Official updates by NHC every 3hrs at 2,5,8 & 11a/pEDT/AST: https://www.nhc.noaa.gov/

[ersatz]

As always, Psychoma, thank you for your detailed information and insight into tropical weather phenomena. But, I wonder about your statement that two storms cannot combine into a bigger storm. There is a lot of discussion currently in the media about the Fujiwhara Effect. A number of articles state that, under the right circumstances, two storms CAN combine into a bigger storm.

I have no background in meteorology, but I remember that Hurricane Sandy combined with a frontal system to create a massively-sized storm. There are examples of hurricanes that combined to create bigger storm effects, such as Connie and Diane in 1955.

[Psychoma]

Fri 21Aug 11aEDT/AST
Winds 45mph(75km/h), moving W 18mph(30km/h), pressure 1007mb
About 210miles(335km) ESE of N Leeward Islands

Latest cone map shows unfavorable track over/near islands. Storms don’t like mountains. Gulf is high uncertainty for location and strength.

[Psychoma]

Originally Posted by ersatz

As always, Psychoma, thank you for your detailed information and insight into tropical weather phenomena. But, I wonder about your statement that two storms cannot combine into a bigger storm. There is a lot of discussion currently in the media about the Fujiwhara Effect. A number of articles state that, under the right circumstances, two storms CAN combine into a bigger storm.

I have no background in meteorology, but I remember that Hurricane Sandy combined with a frontal system to create a massively-sized storm. There are examples of hurricanes that combined to create bigger storm effects, such as Connie and Diane in 1955.

I should rephrase that as two hurricanes/tropical storms don’t combine into a more powerful (wind speed wise) purely tropical system, as in more along the lines of two Cat1’s don’t combine to instantly create a monster Cat5 (even if it’s 2020).

They’re more likely to hurt each other than help. Now tropical systems combining can create a larger diameter size wise storm & the injection of more moisture can help the dominate winner storm. But again purely independent tropical systems are more likely to hurt one or each other when near. But yes other separate weather systems such as Sandy loosing tropical characteristics and combining with front can produce more powerful and larger diameter storms (and recent ie: ex-Kyle combining with North Atlantic Low for large UK Storm the other day). And when you get a Hurricane closer to a high pressure it creates a pressure gradient between the two creating a much larger distance wise wind field on that side of storm.

With two storms there may be more wide spread effects, ie: possibly Higher surf and more rains across a wider region. Still remains to be seen what shape each storm will be and how close they are to each other as we head into next week.

[Psychoma]

Fri 21Aug 5pEDT/AST
Winds 45mph(75km/h), moving W 17mph(28km/h), pressure 1007mb
About 40miles(65km) E of Antigua, TS winds go out up to 115miles(185km) from center, mainly just North side. Still disorganized. Main story for now is rainfall of 1-6in, isolated 8in, especially mountainous areas across the islands through Hispaniola. Guidance has shifted further West in the Gulf of Mexico for early next week.


Watch/Warnings current list:
TS Warning: Puerto Rico, Virgin Islands, Saba, St. Eustatius, St. Maarten, St. Martin, St. Barthelemy, Antigua, Barbuda, St. Kitts, Nevis, Anguilla, Montserrat, North Dominican Republic & Haiti. TS Watch: SE Bahamas, Turks & Caicos.

[Psychoma]

Dr. Kim Wood put together a few GIFs showing tropical cyclones near each other:
https://twitter.com/drkimwood/status...58021755637763

[Psychoma]

Not great looking this evening currently. Posted this on the Hurricane thread with TD14 but Tropical Tidbits video helps explain a lot that's going on now and what the future may hold for Laura. Check that out here, Laura part starts about 7.45min in: https://youtu.be/D2Z1dVxylJo

[Psychoma]

Fri 21Aug 11pEDT/AST
Winds 45mph(75km/h), moving WNW 18mph(30km/h), pressure 1008mb
About 195miles(315km) ESE of San Juan Puerto Rico.
Storm a mess this evening, NHC even says current winds may be generous. So an overnight rainmaker for the islands. Possible we have another center reformation and track adjustment at some point. We'll see what tomorrow brings.

[Psychoma]

Sat 22Aug 2aEDT/AST,1aCDT - Some improvement on satellite/radar near center but like before we'll see if burst of storms holds for more then a few hours.

Watch/Warning changes:
-TS Warning canceled: Antigua, Barbuda, St. Kitts, Nevis, Anguilla, Monserrat
-TS Warning for: SE Bahamas, SE coast of the DR.
-TS Watch for: central Bahamas

[Psychoma]

Sat 22Aug 5aEDT/AST,4aCDT
Winds 40mph(65km/h), moving W 21mph(33km/h), pressure 1007mb
About 70miles(110km) SE of San Juan Puerto Rico.
Storms kept firing overnight. Nice embedded tiny spin on Puerto Rico radar. Air recon to check out what we have later on. NHC cone shifted a little more West with possible hurricane in Gulf by middle of next week.