Tropical Discussion 2025

[Cpv17]

99L could be a player down the road in 9-10 days in the NW caribbean, the GFS has been extremely persistent with developing some sort of tropical entity

Yep, that’s the one we need to watch. Any wave that has a chance to get into the Caribbean has my attention.

[Ptarmigan]

99L could be a player down the road in 9-10 days in the NW caribbean, the GFS has been extremely persistent with developing some sort of tropical entity

Yep, that’s the one we need to watch. Any wave that has a chance to get into the Caribbean has my attention.

Or anything is closer to land. Including Mesoscale Convective System (MCS)/Mesoscale Convective Complex (MCC) that for over land and end up in the Gulf.

[tireman4]

Eastern Tropical Atlantic (AL99):
A tropical wave located several hundred miles southwest of the Cabo
Verde Islands continues to produce a concentrated area of showers
and thunderstorms. Earlier satellite-derived surface wind data
depicted that the system does not have a well-defined center.
Environmental conditions appear marginally favorable for additional
development over the next day or so while the system moves
west-southwestward at around 15 mph and a short-lived tropical
depression could form. By the end of the week, environmental
conditions are expected to become unfavorable for further
development.
* Formation chance through 48 hours...medium...40 percent.
* Formation chance through 7 days...medium...40 percent.

[tireman4]

Near the Leeward Islands in the Tropical Atlantic:
An area of showers and thunderstorms associated with a tropical
wave located a few hundred miles east of the Leeward Islands has
changed little over the past several hours. Environmental
conditions appear conducive for further development of this system,
and a tropical depression is likely to form this weekend while it
moves near or to the north of the northern Leeward Islands.
* Formation chance through 48 hours...medium..40 percent.
* Formation chance through 7 days...high...70 percent.

[tireman4]

Central Atlantic:
A small area of low pressure located about 1200 miles southwest of
the Azores is producing limited showers and thunderstorms.
Upper-level winds are only marginally conducive for development
while the system moves slowly eastward over the next couple of days
* Formation chance through 48 hours...low...30 percent.
* Formation chance through 7 days...low...30 percent.

[tireman4]

Hurricane Erin lashing coastal North Carolina with tropical storm conditions
May be a bit of a wildfire concern in Atlantic Canada, plus the latest on the waves behind Erin
The Eyewall and Matt Lanza
Aug 21








In brief: Hurricane Erin is passing by the Outer Banks today, and it will begin to accelerate out to sea. Coastal flooding will remain an issue into tomorrow for the East Coast, particularly from North Carolina into New Jersey. Mostly wave impacts for Atlantic Canada, but also perhaps some wildfire concerns there too. The rest of the tropics are noisy, but only one wave bears much watching (Bermuda). Also, the latest on upcoming heavy rains in the Plains.

Hurricane Erin

(NOAA/NHC)
Erin is making its closest approach to the U.S. this morning. The very large storm sits about 210 miles east of Cape Hatteras, and it has begun to turn to the north northeast. The tropical storm-force wind field of Erin extends out over 300 miles from the center. Despite the fact that the storm has weakened to about 105 mph this morning, the hurricane-force winds extend out 105 miles from the center. This is a massive storm.


Erin is large and in charge. (Tropical Tidbits)
A 2-to-4-foot surge on the ocean side of the Outer Banks will be ongoing, coupled with powerful waves. It is expected that this evening's high tide cycle will be the highest though, with Duck, NC seeing a water level up to about 7 feet, less than a foot below the 2003 Isabel record there and the highest since a nor'easter in 2022.


Tidal forecast at Duck, NC. (NOAA NWS)
Flooding will be minor to moderate on the Pamlico Sound side of the Outer Banks, with downeast Carteret County seeing the worst this evening around 8:30 PM. High water levels are expected to continue into Friday, and it's likely that some travel will become impossible through today and tonight in the Outer Banks, Ocracoke, and Carteret County.


Even farther up the coast, the tidal flooding will be significant. Cape May, NJ is expecting a peak water level of 8.2 feet this evening, which will be the highest since the "Snowzilla" nor'easter of January 2016. Same goes for Lewes, Delaware.


Tidal forecast at Cape May Harbor (NOAA NWS)
Erin will continue to exit tomorrow, and conditions up and down the East Coast will slowly improve. For Atlantic Canada, the main impact will be rough surf, particularly in Newfoundland and perhaps Nova Scotia, where breaking wave heights could be 3 to 5 meters high. Erin should transition to an extratropical storm by Saturday.

Wildfire concerns?

A minor note, but perhaps a notable one, there will be somewhat enhanced wildfire risk in Atlantic Canada as Erin passes. Note the fire weather danger outlook for today is pretty high to extreme in parts of Newfoundland and even Nova Scotia and New Brunswick.


High to extreme fire weather danger in Atlantic Canada today. (Natural Resources Canada)
Portions of Atlantic Canada remain in severe to extreme drought conditions, so the combination of drier air being wrapped in from the north and gusty winds as the large swath of Erin passes by definitely can enhance fire danger. This is an element of storms that's now on a lot of people's minds in the wake of the tragedy in Maui a couple years ago, as a passing hurricane likely contributed some to drier, windier conditions there. Something for folks in Atlantic Canada to be mindful of over the next 2 to 3 days.

Rest of the tropics
The Atlantic is a multi-colored menagerie of disturbances this morning. We have Invest 99L in the central Atlantic, the tropical disturbance approaching the Caribbean islands that we've been discussing for a few days now, and a little fella in the open Atlantic.


It's a party in the Atlantic! (NOAA NHC)
Let's start from best odds of development to least odds.

The wave approaching the islands with a 70 percent chance of development is looking ragged but stormy today. There's no sign that this is going to develop quickly, but it's starting from a pretty decent baseline.


A tropical disturbance approaching the Leeward Islands will bring thunderstorms and locally heavy rain to the northeast islands this weekend. (Weathernerds.org)
This one is expected to pass northeast of the islands, much like Erin did, so the only impacts will probably be some scattered thunderstorms this weekend. It's hot in Puerto Rico and the Virgin Islands right now, and heat advisories are posted with hot, dry weather and Saharan dust causing hazy conditions. That will change as this passes. From there, it will probably turn straight north toward Bermuda. It seems as though it will turn out to sea before arriving in Bermuda, but interests on that island should continue to monitor this system in the coming days. As you can see below, most European ensemble members miss Bermuda to the east, but it is at least notable that some of the stronger outcomes get a little closer to Bermuda itself. Again, something to monitor at least.


The disturbance near the islands should miss Bermuda to the east, but there are a couple of solutions that are possible that bring it closer to the island. (Weathernerds.org)
We'll keep tabs on this one.

To the east, Invest 99L continues to percolate west of the Cabo Verde Islands. This wave has looked excellent since emerging off Africa, but it has yet to do anything to get it over the hump yet to become a tropical depression.


Invest 99L looks beefy again this morning, as does the wave behind it, but conditions are expected to degrade for development in the Atlantic in a day or two. (Weathernerds.org)
As 99L comes due west, it's likely to run into a wall of wind shear. That should kill any chances of organization. The remnant disturbance should continue west toward the southern Caribbean. Typically, it's a good idea to maintain some degree of vigilance with systems like this, as their ghosts can sometimes be resuscitated once in the western Caribbean. The bulk of what remains of this disturbance may actually end up close to South America, which would essentially wipe out odds of development, even in the western Caribbean. Still, it makes sense to keep tabs on this one in about a week or so, just to ensure it doesn't pull a fast one on us.

The wave behind 99L is not expected to develop and should remain out at sea.

Meanwhile, the NHC tagged a little one this morning. That one near 30N/50W is kind of comedic looking this morning when viewed next to Erin.


I am reminded of "Aladdin" with this. (Weathernerds.org)
That's about it. As Eric noted yesterday, after these systems, we don't exactly have anything noteworthy to home in on. Yesterday's Euro weeklies suggest below average odds of tropical cyclone development in most of the basin for the week of Aug 24-Sept 1.


Below normal odds of development next week in the tropical Atlantic. (ECMWF)
Notably, these odds turn neutral to perhaps even above normal by mid-September. So the first part of September may be calmer than usual, but we're clearly not done with hurricane season yet. But this is good news in the nearer-term.

Heavy rain coming to the Plains?
After a somewhat calmer period of weather in the Southern Plains, we may see a return to more active, wetter weather heading toward next week. The WPC has already issued a slight risk (2/4) for excessive rainfall for next Monday.


Flash flooding will return to the forecast potentially by early next week. (NOAA NWS WPC)
Rain totals are currently forecast to be on the order of 2 to 4 inches over the next 7 days, and there could be some locally higher amounts in parts of Kansas, Oklahoma, or Colorado.


Rain forecast for the next week in the southern Plains. (Pivotal Weather)
We'll keep an eye on this as well.

[tireman4]

Erin

[Stratton20]

Im really becoming more interested in 99L and the intensity models, its very likely already a TS with a pretty impressive structure and sustained deep convection in diurnal minimum ,but the NHC is being so slow to designate this , if it really is a TS, chances of it surviving a track through the caribbean also go up

[sambucol]

Im really becoming more interested in 99L and the intensity models, its very likely already a TS with a pretty impressive structure and sustained deep convection in diurnal minimum ,but the NHC is being so slow to designate this , if it really is a TS, chances of it surviving a track through the caribbean also go up

Why do you think NHC is being so slow about designating it?

[Cpv17]

Im really becoming more interested in 99L and the intensity models, its very likely already a TS with a pretty impressive structure and sustained deep convection in diurnal minimum ,but the NHC is being so slow to designate this , if it really is a TS, chances of it surviving a track through the caribbean also go up

Why do you think NHC is being so slow about designating it?

Cuz it’s not currently a threat to land.

[Stratton20]

Cpv17 Yep, but that might be changing as well speak, i was about to lose attention on this one, now im really interested in it, because it could now possibly hold together in the caribbean and find a way into the gulf, definitely worth watching now

[Cpv17]

2. Central Tropical Atlantic (AL99):
Showers and thunderstorms associated with a tropical wave located
about a thousand miles west-southwest of the Cabo Verde Islands
remain well organized. This system could become a tropical
depression at any time, but the latest satellite-derived wind data
indicate that the system does not have a well-defined circulation
center. The system is expected to move into a less conducive
environment later today through Saturday, but could reach a slightly
more favorable environment again late this weekend into early next
week as it moves westward at 10 to 15 mph over the central tropical
Atlantic and approaches the Lesser Antilles.
* Formation chance through 48 hours...medium...50 percent.
* Formation chance through 7 days...medium...60 percent.

[tireman4]

Erin begins to exit stage right but not before prompting a few more concerns in Atlantic Canada
Wildfire risks in Nova Scotia, New Brunswick, and PEI
The Eyewall and Matt Lanza
Aug 22







In brief: Erin is chugging out to sea now, but not before possibly delivering an enhancement to already extreme wildfire risk in Nova Scotia, New Brunswick, and Prince Edward Island. Rough surf and rip currents will linger on the East Coast and in Atlantic Canada through Sunday. Invest 90L remains worth monitoring for Bermuda. Invest 99L is worth monitoring for the Windward Islands. And flooding chances mix with beneficial rainfall heading into next week in the southern Rockies and Plains.

Hurricane Erin

(NOAA/NHC)
Erin is booking it this morning. The strong, sprawling category one hurricane is moving northeast at over 20 mph. The good news this morning is that all watches and warnings for land have been discontinued. Rough surf and rip currents will continue to impact the East Coast, Bermuda, and Atlantic Canada, but the worst of Erin's impacts to land seem to be over now.


Erin looks like a hurricane that is beginning to undergo extratropical transition, except it's gigantic. (Weathernerds.org)
What's next for Erin? Well it remains a large storm, with a wind field of tropical storm-force over 350 miles now. It should pass well south of land, but gale-force winds are likely in southeast Massachusetts, Nova Scotia, and the Avalon Peninsula in Newfoundland as this passes. Rough surf with waves of 3 to 6 meters may break on the coast of Nova Scotia today and in the Avalon & Burin Peninsulas of Newfoundland later and tomorrow. Even as Erin weakens and turns extratropical in the cooler North Atlantic waters, the size of the gale-force wind field may grow further, keeping Erin a powerful feature on the weather map through the weekend.

Yesterday I noted the wildfire potential with gusty Erin winds blanketing a very dry Atlantic Canada. Well, the fire risk today at least seems pretty noteworthy in Nova Scotia, PEI, and parts of New Brunswick, with "extreme risk" drawn in those areas.


Extreme fire risk for much of Atlantic Canada outside of Newfoundland today. (Natural Resources Canada)
That risk should remain and expand into Newfoundland tomorrow. For some areas, the risk may diminish as Erin passes, particularly for Newfoundland. In Nova Scotia, New Brunswick, and PEI, however, the risk may stay at extreme levels through the entire weekend. A rare situation for this part of the world.

Erin's remnants will park themselves south of Iceland for a time before probably moving into Europe as a (much weaker) storm next week.

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Invest 90L
Let's work our way back south now to Invest 90L. This one continues to lack much organization today, but models continue to insist it will eventually get its act together.


Invest 90L has very broadly disorganized thunderstorms, but that's it at this point. (Weathernerds.org)
Over the next few days, this broader area may try to consolidate some, and we should see gradual development into a tropical depression or tropical storm. Invest 90L will track around the western edge of high pressure just west of the Azores, meaning it will continue on a north-northwest or northward trajectory. Model guidance at this point seems to suggest it will stay east of Bermuda on its way north, but we'll continue to watch this, particularly once we (presumably) get some development out of this area.


Tropical model guidance has a relatively tight spread keeping 90L east of Bermuda, but it's close. (Tropical Tidbits)
Interests in Bermuda should continue to monitor 90L over the next couple days. We do not expect this one to explode and rapidly intensify to a high-end storm like Erin did. But we could see it quickly come together as a tropical storm.

Invest 99L
Backing off to the south and east now, we look at Invest 99L. This one has had the opposite problem of 90L. Models have insisted it would eventually succumb to shear and dry air, and it's been as resilient a wave as we've seen all season. Well, Invest 99L's luck may be running out.


Invest 99L is looking much less organized and much uglier than it has all week. (Tropical Tidbits)
Over the next 3 to 4 days, Invest 99L will continue to have a puncher's chance at perhaps sneaking into tropical depression status before likely getting ripped up again in the Caribbean. Interests in the islands should at least keep an eye on this, particularly for the Windward Islands. But this seems like mostly just a scattered heavy rainmaker right now. Beyond the islands, it seems likely that this will remain buried in the Caribbean or end up moving ashore in Central America eventually as a remnant disturbance. But we'll continue to watch in case something should change.

Flooding risks
Yesterday saw a flash flood emergency, our first in quite some time, this one in Roanoke, Virginia. Read Kevin Myatt's always excellent coverage in the Cardinal News for more on that event. But 3.38 inches of rain in an hour is more like Gulf Coast style than Appalachia. Very impressive stuff.

Flash flooding risk today will be mainly in Georgia and South Carolina back across the Gulf Coast, as a stationary front is draped across the region. But as we go into next week, we continue to see a pretty strong signal for heavy rain in the Plains. A slight risk (2/4) for excessive rainfall and flooding remains painted on the maps for Monday between the Front Range and Kansas & Oklahoma.


Slight risks for heavy rain (2/4) are in place on Monday from the Rockies to the Plains. (NOAA WPC)
Colorado Springs, Wichita, Tulsa, and Oklahoma City are all included here. For Tuesday, that risk shifts mostly back into Colorado and New Mexico. Rain totals over the next week continue to look quite healthy in these areas, with perhaps 1 to 4 inches in Colorado and parts of New Mexico and 3 to 6 inches in Kansas and Oklahoma.


Rain totals over the next week are stout between the Rockies and Plains. (Pivotal Weather)
Considering the Rio Grande has dried up to a trickle or worse, any amount of rain that could find its way into the system would be beneficial.

[Stormlover2020]

Icon is now on board

[Stratton20]

yup, TS in the western caribbean

[tireman4]

Levi Cowan

[tireman4]

000
WTNT35 KNHC 222030
TCPAT5

BULLETIN
Post-Tropical Cyclone Erin Advisory Number 46
NWS National Hurricane Center Miami FL AL052025
500 PM AST Fri Aug 22 2025

...ERIN BECOMES POST-TROPICAL, THIS IS THE LAST ADVISORY...
...SWIMMING AT MANY U.S. EAST COAST BEACHES IS LIKELY TO REMAIN
DANGEROUS THROUGH THE WEEKEND...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...40.0N 59.7W
ABOUT 605 MI...970 KM NNE OF BERMUDA
ABOUT 375 MI...605 KM SSE OF HALIFAX NOVA SCOTIA
MAXIMUM SUSTAINED WINDS...90 MPH...150 KM/H
PRESENT MOVEMENT...ENE OR 65 DEGREES AT 33 MPH...54 KM/H
MINIMUM CENTRAL PRESSURE...957 MB...28.26 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 500 PM AST (2100 UTC), the center of Post-Tropical Cyclone Erin
was located near latitude 40.0 North, longitude 59.7 West. The
post-tropical cyclone is moving toward the east-northeast near 33
mph (54 km/h). This general motion with an increase in forward
speed is expected later today, followed by a turn back to the
northeast on Sunday. On the forecast track, the center of Erin
will pass south of Atlantic Canada today and tonight, and then race
across the north Atlantic waters.

Maximum sustained winds remain near 90 mph (150 km/h) with higher
gusts. Erin is likely to remain a large and powerful
hurricane-force low pressure system through the weekend.

Hurricane-force winds extend outward up to 125 miles (205 km) from
the center and tropical-storm-force winds extend outward up to 435
miles (705 km).

The estimated minimum central pressure is 957 mb (28.26 inches).


HAZARDS AFFECTING LAND
----------------------
Key messages for Erin can be found in the Tropical Cyclone
Discussion under AWIPS header MIATCDAT5 and WMO header WTNT45 KNHC.

WIND: Gale-force wind gusts are possible along portions of the
coast of Nova Scotia today and the Avalon Peninsula of Newfoundland
on Saturday.

SURF: Swells generated by Erin will affect the Bahamas, Bermuda,
the east coast of the United States, and Atlantic Canada during the
next few days. These rough ocean conditions are expected to
cause life-threatening surf and rip currents. Please consult
products from your local weather forecast office for more
information.

A depiction of rip current risk for the United States can be found
at: hurricanes.gov/graphics_at5.shtml?ripCurrents

STORM SURGE: Some coastal flooding is expected at times of high
tide along portions of the U.S. Mid-Atlantic and New England coasts
through tonight, making some roads impassable. See updates from
your local National Weather Service office for details.


NEXT ADVISORY
-------------
This is the last public advisory issued by the National Hurricane
Center on this system. Additional information on this system can be
found in High Seas Forecasts issued by the National Weather
Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and
online at ocean.weather.gov/shtml/NFDHSFAT1.php

$$
Forecaster Blake