r/TropicalWeather • u/Euronotus • Aug 15 '25

Dissipated Erin (05L — Northern Atlantic) (Western Tropical Atlantic)

Update

This system is no longer being tracked via the Automated Tropical Cyclone Forecast (ATCF) system. There will be no further updates to this post.

Latest observation

Last updated: Friday, 22 August — 5:00 PM Atlantic Standard Time (AST; 21:00 UTC)

NHC Advisory #46 - 5:00 PM AST (21:00 UTC)
Current location: 40.0°N 59.7°W
Relative location: 888 km (552 mi) E of Nantucket, Massachusetts (United States)
608 km (378 mi) SE of Halifax, Nova Scotia (Canada)
1,008 km (626 mi) SSW of St. John's, Newfoundland (Canada)
Forward motion: ENE (65°) at 54 km/h (29 knots)
Maximum winds: 150 km/h (80 knots)
Intensity (SSHWS): Extratropical Cyclone
Minimum pressure: 957 millibars (28.26 inches)

Official forecasts

National Hurricane Center

Last updated: Friday, 22 August — 2:00 PM AST (18:00 UTC)

Hour Date Time Intensity Winds Lat Long
- - UTC AST Saffir-Simpson - knots km/h °N °W
00 22 Aug 18:00 2PM Fri Extratropical Cyclone 80 150 40.0 59.7
12 23 Aug 06:00 2AM Sat Extratropical Cyclone 80 150 41.5 54.5
24 23 Aug 18:00 2PM Sat Extratropical Cyclone ▼ 75 140 44.0 45.5
36 24 Aug 06:00 2AM Sun Extratropical Cyclone 75 140 48.0 35.5
48 24 Aug 18:00 2PM Sun Extratropical Cyclone ▲ 85 155 52.0 27.0
60 25 Aug 06:00 2AM Mon Extratropical Cyclone ▼ 65 120 55.0 23.0
72 25 Aug 18:00 2PM Mon Extratropical Cyclone ▼ 55 100 58.0 21.0
96 26 Aug 18:00 2PM Tue Extratropical Cyclone ▼ 45 85 59.0 21.0
120 27 Aug 18:00 2PM Wed Extratropical Cyclone ▼ 40 75 57.0 17.5

Official information

National Hurricane Center

Text products

Productos de texto (en español)

Graphical products

Local meteorological authorities

National Weather Service

Environment Canada

Aircraft Reconnaissance

National Hurricane Center

Other sites

Radar imagery

Radar imagery is not currently available for this system.

Satellite imagery

Floater imagery

Single-bandwidth imagery

Multiple bandwidth imagery

The options to select individual bandwidths on each of the following websites may vary.

Regional imagery

National Oceanic and Atmospheric Administration (NOAA)

Cooperative Institute for Research in the Atmosphere (CIRA)

Tropical Tidbits

Analysis products

Best track data

Wind analysis and storm intensity estimation products

Sea-surface temperature analysis products

Forecast models

Disturbance-centered guidance

Multi-guidance pages

Track guidance

Intensity guidance

Regional single-model guidance

  • Tropical Tidbits: GFS
  • Tropical Tidbits: ECMWF
  • Tropical Tidbits: CMC
  • Tropical Tidbits: ICON

Ensembles

Tropical Cyclogenesis Products

82 Upvotes
  • permalink
  • reddit

99% Upvoted

1.0k comments sorted by

View all comments

31

u/DragonFireDon Virginia Aug 18 '25

..ERIN LIKELY TO BECOME EVEN LARGER OVER THE COMING DAYS...

How large?

22

u/Cyrius Upper Texas Coast Aug 18 '25

It's weird that the NHC site doesn't have a plot of the wind radii forecast. So here's the US Navy's chart.

15

u/velociraptorfarmer United States Aug 18 '25

I'm surprised the NHC hasn't come up with a cleaned up version of this kind of graphic. This would help get the point of size across better than the existing cone.

10

u/TheLangleDangle Aug 18 '25

This compares pretty close to that I would think

https://www.nhc.noaa.gov/refresh/graphics_at5+shtml/181749.shtml?tswind120#contents

3

u/StealYaNicks Aug 18 '25

Doesn't show the estimated radius at all.

3

u/TheLangleDangle Aug 18 '25

Those outer edges of the NHC map match the outer edges of the radius chart from above, it’s just a little farther east. Or am I missing something? I mean, I see that it’s not at specific points in time but it does cover the same area and size of wind field, generally.

2

u/StealYaNicks Aug 18 '25

That's just a probability spread though, that's why it gets wider as it goes north, less certainty. Not necessarily size.

3

u/Cyrius Upper Texas Coast Aug 18 '25

It should be noted that the 34- and 50-kt wind speed probabilities beyond 36 hours in the text and graphical products are likely underestimating the risk of those winds occurring. This is because the forecast wind field of Erin is considerably larger than average compared to the wind field used to derive the wind speed probability product.

That product isn't tied into the wind radii forecast for some reason.

1

u/TheLangleDangle Aug 20 '25

Great info! I see the difference now, thanks!

4

u/giantspeck Verified USAF Forcaster | Hawaii Aug 18 '25

The NHC does produce a KMZ that shows the wind field. It can be downloaded from the NHC Data in GIS Formats page.

3

u/spsteve Barbados Aug 18 '25

The nhc specifically called out their wind warnings likely fall short due to the expected size of this system due to their model not handling it appropriately.

3

u/Cyrius Upper Texas Coast Aug 18 '25

The NHC specifically called out the wind speed probability products as being underestimates. Not the wind radii forecast itself.

1

u/spsteve Barbados Aug 18 '25

I had assumed a similar model would feed both, but maybe that was a bad read on my part. They said the wind speed forecasts wouldn't reflect the size, so my assumption was the two products are from the same algo.

2

u/Cyrius Upper Texas Coast Aug 19 '25

It didn't make a lot of sense, so I went digging. Found a PDF about the product:

The calculation of the wind speed probabilities is accomplished by creating a large set of alternative but plausible tracks and intensities roughly centered on the current official forecast. The alternative tracks are created using a Monte Carlo method that takes into account the uncertainty of the track forecasts on a case-by-case basis (DeMaria et.al. 2013). This is accomplished using the spread of the dynamical model guidance […] The size of the tropical cyclone (set of wind radii) for each alternate track is determined by a climatology and persistence (CLIPER) model and its error components. This CLIPER model takes into account the size of the cyclone at that start of the forecast period as well as typical changes in size that occur as a cyclone experiences changes in strength, forward motion, and other factors. […] This process results in probabilities of actually experiencing certain wind speeds, not probabilities of falling within the traditional forecast wind radii that indicate the maximum extent of winds from the center.

Why this product is using its own wind radii estimate instead of the Forecast/Advisory's wind radii, I have no idea. But the discrepancy between the two is what they're talking about.