Thunder44's Helene 8am Thurs Forecast: Turns North/Weakens

[Thunder44]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org For Official Information please refer to the NHC and NWS products.

On this thread, I'm going to post my forecast and thoughts behind it, from time to time on this thread on what I think Helene will do. To avoid confusion, I'm not going to do any of my own upgrades or changes on initial intensity or position. They will be in line with TPC statements. Any commets are welcome.

6:30am Discussion:

As of the 5am Advisory issued by NHC. TS Helene currently at 13.7N 34.7W and is moving west at 22mph, with maximum sustained winds of 35kts.

My forecast track is based on the idea that Helene will be moving around the periphery of the subtropical ridge over the East Atlantic at generally the same W to WNW motion. After 48hrs the storm should turn NW as it moves into the weakness in the ridge over Central Atlantic. However after 72hrs most models show some ridging building back again to the north, behind Hurricane Gordon, which is moving NE in the open waters of the Central Atlantic. This will cause Helene to slow down significantly and turn the storm back to the W or WNW for awhile. The forecast track reflects this but is too the left of most of guidance, especially the GFS and GFDL, as many are already taking Helene NW not far from where they initialized.

The upper-level environment through 5 days looks favorable for further development. The SHIPS takes Helene to hurricane strength by 36hrs, while the GFDL does the same by 48hrs. Then both models take it too 86kts and 90kts by 120hrs, respectively. Given that the circulation is still large my intensity forecast will be more in line with GFDL through 48hrs, then intensification will be at a faster rate as the circulation eventually becomes more compact and moves over warmer SSTs.

Forecast Points and Intensity:

Initial: 13.7N 34.7W 35kt
12hrs: 14.3N 38.6W 40kt
24hrs: 15.2N 42.1W 50kt
36hrs: 16.1N 45.6W 55kt
48hrs: 17.4N 48.9W 60kt
72hrs: 19.4N 51.9W 70kt
96hrs: 20.4N 53.6W 80kt
120hrs: 20.8N 55.0W 90kt



I will have update around noon.

[cycloneye]

Congrats for your first ever forecast,It looks very good,like a proffesional forecaster with all the factors discussed,and the google graphic.

[Thunder44]

Congrats for your first ever forecast,It looks very good,like a proffesional forecaster with all the factors discussed,and the google graphic.

Thanks.

[Evil Jeremy]

update time!

[Thunder44]

update time!

Give me a few minutes.

[Thunder44]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org For Official Information please refer to the NHC and NWS products.

11:30am Update:

I have shifted the track southward through the first 24hrs, as the center was relocated further south this morning. Otherwise the basically forecast reasoning remains the same and forecast track is the same until 96hrs. The 6z runs of the GFS and GFDL have shifted little further west and it appears that the NOGAPS has the best handle on this storm so far. Some of the NHC models have shifted west as well. After 96hrs global models show a shortwave trough moving into into Western Atlantic and turn the storm more northward. I will show a turn to the NW at 120hrs.

Latest SHIPS have Helene reaching hurricane by 36hrs and at 92kts, then holds about steady after between 96 and 120hrs.. The intensity forecast is little more conservative for now.

So far it appears that the center will stay well north and east of the Lesser Antilles, but a track closer to the NE Carribean Islands is possible if the center keeps going south of forecast points.

Initial 13.4N 36.8W 40kt
12hrs 14.5N 40.2W 45kt
24hrs 15.5N 43.6W 50kt
36hrs 16.7N 47.0W 55kt
48hrs 18.1N 50.4W 65kt
72hrs 19.7N 52.5W 75kt
96hrs 20.0N 54.3W 85kt
120hrs 22.0N 56.0W 85kt

[Thunder44]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org For Official Information please refer to the NHC and NWS products.


6pm Update:

At the 5pm Advisory, NHC placed the center of TS Helene currently at 14.2 N...37.6 W and now moving to the WNW at 16mph. Maximum sustained winds are estimated 40kts.

TS Helene has not gotten much better organized this afternoon and has slowed it’s forward motion. The forecast reasoning has not changed from this morning. It just a matter of where Helene eventually begins her recurvature out in the Central Atlantic which appears more likely as each passing the day approaches. The GFS and GFDL have continued come westward but appeared to still be too far east. They are not properly analyzing the expansion of the ridge occurring now over the Central Atlantic south of Hurricane Gordon. The NOGAPS and the UKMET are the farthest west with Helene, and turn the storm NW into the weakness in the ridge near between 50W and 55W by 72hrs and then they have a slower stair-step motion well NE of the Northern Leeward Islands. The ECMWF and CMC tracks are in somewhere in between. I favor the NOGAPS and the UKMET or slightly to the left. The forecast track is slower and has been adjusted north for the first 24hrs due to the relocation of the center further north and then basically remains unchanged, with no changes to the forecast intensity.

At this time it doesn’t appear that Helene will have much impact to the Carribean Islands. A large deep-layer trough forecast by the models to be over the Eastern Seaboard and West Atlantic after five days, should also prevent landfall in the US mainland.

Forecast Points and Intensity:

Initial 14.2 N 37.6 W 40kt
12hrs 14.8N 40.3W 45kt
24hrs 15.5N 43.6W 50kt
36hrs 16.7N 47.0W 55kt
48hrs 18.1N 50.4W 65kt
72hrs 19.7N 52.5W 75kt
96hrs 20.0N 54.3W 85kt
120hrs 22.0N 56.0W 85kt

[Thunder44]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org For Official Information please refer to the NHC and NWS products.


7am Forecast

Discussion:

As of the 5am Advisory, NHC has placed the center currently at 15.0N 40.3W and is moving WNW at 15mph. Maximum sustained winds are at 40kts with a pressure of 1003mb.

TS Helene appears to be continuing to move to the WNW at with no change in intensity. Although over the last few hours it has organized more convection over the center.

Overnight the 0z global models continued show a weakness in the subtropical ridge that will cause Helene to eventually turn NW. However there is still disagreement on where this turn will happen. The GFS and GFDL insist turning the storm NW from almost where it is now and that appears to be wrong. The UKMET and NOGAPS are still the farthest left of the guidance, while the ECMWF and CMC remain in the middle, although they have shifted somewhat to left as well. Since the overall consensus of the guidance continues to shift towards the west, the forecast track will follow the the UKMET and NOGAPS solution through 72 hrs and will be shifted to the north and will be slower as well.

After that NOGAPS diverges from the UKMET somewhat by showing the storm track slowly off to the west, as it weakens shortwave trough in Western Atlantic and moves it NE and builds back the ridge to the north of Helene again. While the UKMET continues to bring the storm NW. At this time I don’t know whether to believe this solution or not. But I will forecast a slow WNW movement to compromise both solutions for now.

It appears that Helene’s intensification process will continue to be slow through the forecast period due to it’s large size and entraining of the SAL, but upper-level winds and warmer SST to should allow to reach to hurricane strength by 48hrs and reach Cat 2 status by 96hrs. After 96hrs SW shear could be on the increase with the trough in the West Atlantic, therefore I show no further strengthen at 120hrs.

Forecast Points and Intensity:
Initial 15.0N 40.3W 40kt
12hrs 16.0N 42.9W 45kt
24hrs 17.3N 45.3W 50kt
36hrs 18.5N 47.7W 55kt
48hrs 18.9N 48.5W 65kt
72hrs 20.0N 50.0W 75kt
96hrs 20.8N 51.6W 85kt
120hrs 21.4N 53.4W 85kt

[Thunder44]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org For Official Information please refer to the NHC and NWS products.

11am Update:

As of the 11am Advisory, the NHC has placed the center of TS Helene at 15.8N 41.4W and is moving to the WNW at 12mph. Maximum sustained winds have increased to 60mph with a pressure of 1000mb.

I adjusted the track the first 24 hours to account for the center being placed a little further north. The intensity will adjusted higher for the first 72hrs to account for further intensification this morning than expected, and will probably become a hurricane within the next 24hr to 36hrs. Otherwise there are no other changes to the forecast track or intensity at this time. I will be reviewing the 12z model guidance this afternoon and I should have a new forecast out sometime this evening.

Forecast Points and Intensity:

Initial 15.0N 40.3W 50kt
12hrs 16.3N 42.9W 55kt
24hrs 17.3N 45.3W 60kt
36hrs 18.5N 47.7W 65kt
48hrs 18.9N 48.5W 70kt
72hrs 20.0N 50.0W 80kt
96hrs 20.8N 51.6W 85kt
120hrs 21.4N 53.4W 85kt

[Thunder44]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org For Official Information please refer to the NHC and NWS products.

7pm Forecast: Some Changes But No Threat to Land

As of the 5pm Advisory, the NHC has placed the center of TS Helene at 16.7N 42.8W and is moving toward the WNW at 15mph. Maximum sustained winds have increased to 60kts and the pressure is estimated at 992mb.

TS Helene has been intensifying today much faster than forecasted. On satellite imagery, the storm continues to get better organized with an hints of eye trying to form and deep convection around the center. Satellite estimates are nearing hurricane strength and Helene will likely become hurricane later tonight.

As it has intensified today, it has also gained more latitude as responds to weakness in the ridge in the at 200mb to 300mb level. This will be one reason why caused my forecast track will be shifted farther to the north. The UKMET and NOGAPS continue to be left side than all the guidance, and the GFS and GFDL continue be on the right, and ECMWF and CMC in the middle. Although the spread of the guidance is decreasing and the models generally show a WNW to NW track of Helene over the next five days, with a slow down in forward speed after 3 days. Since the storm is already moving a little further north than expected, the UKMET and NOGAPS will likely be too far south after 24hrs and forecast track is shifted closer to model consensus.

Helene has become more compact, and developing an inner core and upper-level conditions are favorable. Therefore intensification at a faster rate seems more likely now. I’ve increased the forecast intensity through the five day period. I expect Helene to become a major Cat 3 hurricane by 72hrs and then level off as shear possibly increases from the shortwave trough in the Western Atlantic.

On the current forecast track, Helene will be passing about 600 miles from the NE Leeward Islands in five days. Any impacts from the storm appear very unlikely.

Initial 16.7N 42.8W 60kt
12hrs 18.0N 14.2W 65kt
24hrs 19.4N 47.5W 75kt
36hrs 20.6N 49.1W 85kt
48hrs 21.6N 50.5W 90kt
72hrs 22.8N 52.5W 100kt
96hrs 23.4N 54.0W 100kt
120hrs 25.1N 57.0W 100kt

[Thunder44]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org For Official Information please refer to the NHC and NWS products.

8am Forecast: No Threat to Land

Discussion:

As of the 5am Advisory, the NHC has placed the center of TS Helene at 17.9N 44.7W and is moving WNW at 15mph. Maximum sustained winds remain at 60kts and the pressure is estimated at 992mb.
Helene did not organize well enough last night to be upgraded to hurricane status, but it will probably become a hurricane later today. I see nothing to prevent this happen. Upper-level wind remain favorable for further development and dry air or SAL entrainment appears to be minimal.

The new forecast track has not changed much from the previous one, except that it has been extended. Some of the models have shifted to the west last night but the consensus remains about the same. Helene is still expected to move WNW to NW the next 4 days into weakness in the subtropical ridge in Central Atlantic, already created by Hurricane Gordon. The shortwave trough along the US Mid-Atlantic Coast now will move SW in the Western Atlantic and create another weakness in the next few days. Then after Day Helen will be in between a larger and stronger trough moving into the Western Atlantic and a strenghtening ridge in the East Atlantic. This should start to recurve Helene out in the open Atlantic. After 96hrs the storm should turn NNW.

The Ships now only take Helen to about 78kts by five days. However, the GFDL is much stronger and takes it near Cat 3 hurricane status. The global models also seem to forecast a major hurricane in the Central Atlantic in the 4 to 5 days. So I will not change forecast intensity change much from the last forecast.

At this time it looks the storm will pass east of Bermuda beyond 5 days, but it a closer pass can’t be ruled out yet, if models continue they westward shifts. I just viewed the 6z GFS, but that was not considered into this forecast.

I will have another forecast out sometime this evening.

Forecast Points and Intensity:
Initial 17.9N 44.7W 60kt
12hrs 19.4N 47.5W 65kt
24hrs 21.0W 49.6W 75kt
36hrs 22.0N 51.2W 85kt
48hrs 22.6N 52.1W 95kt
72hrs 23.9N 54.8W 100kt
96hrs 25.4N 57.3W 100kt
120hrs 28.5N 58.9W 100kt

[Thunder44]

11am Update:

As of the 11am Advisory NHC has upgraded Helene to a hurricane with maximum sustained winds of 65kts and is now moving NW at 15mph. This update is just to change the current status of his storm. No changes will be made to the forecast at this time.

[Thunder44]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org For Official Information please refer to the NHC and NWS products.

8pm Forecast

Discussion:

As of the 5pm Advisory, the NHC placed the center of Hurricane Helene at 19.3 N...46.3 W and moving to the NW at 13 mph. Maximum sustained winds remain at 75 mph with a pressure at 987 mb.

There is significant spread in the global model guidance again today, as some models want to recurve Helene out to sea, while some want to bring further NW during the 3 to 5 day period. All models seem to agree on general WNW to NW movement through 72hrs. Then the UKMET, CMC, and GFDL all turn the storm northward before reaching 60W. The ECMWF and NOGAPS generally take storm NW towards Bermuda, and the GFS is farther south. At this time the forecast track will be shifted further north as the Helene has been generally running a little to right side of the track today and many of the southern models. I have the storm moving NW through 72hrs and then turning to NNW after that. This is much further north than the ECMWF, NOGAPS, and GFS, but is still a little to the left of the other models. It’s possible that the models will shift further west tonight, if that’s the case the track may need to be shifted much further left tomorrow.

Despite what track this storm takes the GFDL and the global models still make this storm into a major hurricane. The intensity forecast will gradually show Helene reaching 100kts by 72hrs then maintain that intensity afterwards.

Forecast Points and Intensity:

Initial: 19.3N 46.3W 65kt
12hrs: 20.1N 48.7W 75kt
24hrs: 22.3N 50.7W 80kt
36hrs: 23.4N 52.4W 85kt
48hrs: 24.5N 54.4W 90kt
72hrs: 25.5N 55.9W 100kt
96hrs: 28.6N 57.5W 100kt
120hrs: 31.0N 59.0W 100kt

[Thunder44]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org For Official Information please refer to the NHC and NWS products

8am Sun Forecast:

As of the 5am Advisory, the NHC placed the center of Helene currently at 20.0N 48.2W and is moving NW at 8kts. Maximum sustained winds have increased to 75kts and minimum pressure is estimated at 979mb.

Not much time to discuss the sypnotics this morning. Basically, my forecast track is little further to the left and is closely follows the UKMET and NOGAPS after 72hrs, which is also close to the consensus track and NHC forecast. I still expect to Helen to become a major hurricane by 48hrs, but some weakening is shown after 72hrs, for increasing shear potential.

I may update later this morning or this afternoon with a more in-depth discussion. My new forecast will come out sometime this evening.

Forecast Points and Intensity:

Initial 20.0N 48.2W 75kt
12hrs 21.1N 49.9W 80kt
24hrs 22.3N 51.6W 85kt
36hrs 23.3N 53.4W 90kt
48hrs 23.8N 55.3W 100kt
72hrs 25.2N 57.5W 95kt
96hrs 28.0N 58.8W 90kt
120hrs 30.0N 59.5W 85kt

[Thunder44]

11am Update:

This update is just to make changes to intensity forecast to account for the significant change in current strength this morning. Helene is now a Cat 2 hurricane with winds of 90kts, as of the 11am Advisory from the NHC. I now expect Helene to become a strong Cat 3 hurricane by 48 hours with winds near 110kts (125mph).

Forecast Points and Intensity:

Initial 20.5N 49.0W 90kt

12hrs 21.1N 49.9W 95kt

24hrs 22.3N 51.6W 100kt

36hrs 23.3N 53.4W 105kt

48hrs 23.8N 55.3W 110kt

72hrs 25.2N 57.5W 105kt

96hrs 28.0N 58.8W 100kt

120hrs 30.0N 59.5W 90kt

[Thunder44]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org For Official Information please refer to the NHC and NWS products

8pm Forecast: Helene Strengthens

As of the 5pm Advisory, the NHC placed the center of Hurricane Helene at 21.2N 49.3W and is moving NW at 8kts. Maximum sustained winds remain near 90kts and the minimum pressure at 970mb.

Helene has significantly strengthened today to a strong Cat 2 hurricane, based on satellite estimates and a NOAA Research plane investigating the storm for awhile this afternoon. Helene appears to still be strenghtening this evening as well and the upper-level winds look to be favorable for more strengthening during the next 36hrs to 48hrs and expect to Helene to be a strong Cat 3 hurricane. It’s possible she could get even stronger, but due it’s large size, strenghtening will be at more steady pace, before shear being forecast by the SHIPS and several global models increases after 48hrs and moves over slightly cooler water as well. Gradual weakening is shown in the forecast afterwards.

The track of Helene is most complicated part of this forecast. The models continue to have widespread differences in their tracks of Helene during the 3 to 5 day period, as the models handle several synoptic features differently.

The 12z runs of the GFS, NOGAPS, and now the UKMET, take the storm more westward south of Bermuda as they weaken and move out the first shortwave trough off the Mid-Atlantic coast now, and build a ridge to the north Helene, and also show the second larger trough missing it. The ECMWF, CMC, MM5, and GFDL all recurve the storm well east of Bermuda, as they are stronger with the first shortwave, and keeps the weakness in the ridge longer, causing the storm move further north, before the ridge builds back north again. Then the second larger trough turns finally takes it out NNE into the North Atlantic. The overall consensus of the models have been shown a west trend over the last few days and it will not surprise me to see a further west adjustment in some of the “eastern solutions” tonight. Hopefully they will have better handle on the system off the Mid-Atlantic coast tonight, which appears to be moving ESE at this time.

For now the forecast track will be shifted little farther west to follow the CONU track and is also close to the current NHC track. In five days, I have storm about 250 miles SE of Bermuda.

Forecast Points and Intensity:

Initial 21.2N 49.3W 90kt
12hrs 22.0N 50.0W 100kt
24hrs 22.5N 51.5W 105kt
36hrs 23.0N 53.0W 110kt
48hrs 23.5N 54.5W 110kt
72hrs 24.5N 57.5W 105kt
96hrs 27.5N 59.5W 90kt
120hrs 30.5N 61.0W 90kt

[Scorpion]

Why 90 kts? Its about 105 kts now.

[Thunder44]

Why 90 kts? Its about 105 kts now.

That's from the 5pm Advisory from NHC. I'm using their initial positions and intensity. I'm not doing my own estimates here.

[Evil Jeremy]

you should!

[Thunder44]

you should!

I don't want to confuse anybody and I don't want to get into that debate here either.