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13-10-2020, 15:25   #241
Gaoth Laidir
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September was a busy month, with a record ten named storms forming. However, hurricanes-wise it was more in line with the long-term average, with 4 hurricanes forming, 1 of which was major. It continues the trend of this season, which has had a high number of named storms (25), but most of which were weak and short-lived, with a relatively low fraction becoming hurricanes (9) and major hurricanes (3).

September 2020 stats (1981-2010 average in brackets)
Named storms: 10 (4)
Hurricanes: 4 (3)
Major hurricanes: 1 (1)

2020 season stats up to 13 October (1981-2010 stats for this point in season in brackets)
Named storms: 25 (10.2)
Named storm days: 86.75 (49.5)
Hurricanes: 9 (5.2)
Hurricane days: 22.75 (20.4)
Major Hurricanes: 3 (2.4)
Major Hurricane Days: 5.75 (5.6)
Total ACE: 123.1 (89.7)

Quote:
Monthly Tropical Weather Summary
NWS National Hurricane Center Miami FL
800 AM EDT Thu Oct 1 2020

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

Tropical cyclone activity in the Atlantic basin during the month of
September was very busy and set a record for the most named storms
forming in a month. Ten named storms formed, with Omar forming from
a tropical depression that began in late August. Four of the storms
became hurricanes with one, Hurricane Teddy, reaching major
hurricane strength. Based on a 30-year climatology (1981-2010),
four named storms typically form in the basin in September, with
three of them becoming hurricanes, and one of them becoming a major
hurricane.

In terms of Accumulated Cyclone Energy (ACE), which measures the
strength and duration of tropical storms and hurricanes, activity
in the basin so far in 2020 has also been above average, about 25
percent above the long-term mean.

Reports on individual cyclones, when completed, are available at
the National Hurricane Center website at
http://www.hurricanes.gov/data/tcr/i...2020&basin=atl

Summary Table

Name | Dates | Max Wind (mph)
---------------------------------------------------
TS Arthur | 16-19 May | 60*
TS Bertha | 27-28 May | 50*
TS Cristobal | 1-9 Jun | 60
TS Dolly | 22-24 Jun | 45
TS Edouard | 4-6 Jul | 45
TS Fay | 9-11 Jul | 60
TS Gonzalo | 21-25 Jul | 65
H Hanna | 23-27 Jul | 90
H Isaias | 30 Jul- 5 Aug | 85
TD Ten | 31 Jul- 1 Aug | 35
TS Josephine | 11-16 Aug | 45
TS Kyle | 14-16 Aug | 50
MH Laura | 20-28 Aug | 150
H Marco | 20-25 Aug | 75
H Nana | 1-4 Sep | 75
TS Omar | 31 Aug- 5 Sep | 40
H Paulette | 7-22 Sep | 105
TS Rene | 7-14 Sep | 50
H Sally | 11-17 Sep | 105
MH Teddy | 12-22 Sep | 140
TS Vicky | 14-17 Sep | 50
TS Wilfred | 18-20 Sep | 40
SS Alpha | 18 Sep | 50
TS Beta | 17-22 Sep | 60
---------------------------------------------------

* Denotes a storm for which the post-storm analysis is complete.

Last edited by Gaoth Laidir; 13-10-2020 at 15:33.
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13-10-2020, 19:35   #242
Oneiric 3
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Rumour has it that the Tropical Atlantic could flare up again towards the end of the month as something called the 'MJO' shifts to the west.
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19-10-2020, 12:33   #243
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Not really

Fortunately this forecast did not bear much fruit. As a Hatteras junkie I saw little evidence of hurricanes this year.
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19-10-2020, 17:43   #244
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Tropical Storment Epsilon has formed from a non-tropical low that's been loitering around the mid-Atlantic for the past week. It should become a hurricane with in a few days as it moves northwestwards near Bermuda, though ocean heat content will be very marginal for that.

Last edited by Gaoth Laidir; 19-10-2020 at 19:20.
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19-10-2020, 23:06   #245
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There's a wide spread in intensity forecasts for Epsilon as it will be in very marginal waters. It still has a lot of organising to do as it meanders over the warmest waters over the next day before heading over much lower heat content on its way close to Bermuda.





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19-10-2020, 23:15   #246
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These are all the systems that have formed in the 14-day period October 14th-27th since the 1966 (from here). Any major hurricanes that form at this time of the year do so in the Caribbean.

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20-10-2020, 09:14   #247
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Epsilon has the structure of an extratropical storm, yet they're still classifying it as a tropical storm. In any case it's becoming more unlikely that it will reach hurricane-force as it moves over colder waters.

Quote:
Tropical Storm Epsilon Discussion Number 4
NWS National Hurricane Center Miami FL AL272020
1100 PM AST Mon Oct 19 2020

Water vapor imagery indicates that Epsilon has been interacting with
a shear line/dissipating cold front from the north and with a
negatively tilted upper-level trough from the south. Furthermore, a
pronounced dry slot has developed in the eastern semicircle, which
has severed the convective band that had been wrapping about
three-fourths of the way around the circulation. Overall, the cloud
pattern more closely resembles that of an occluded extratropical
low, with a small inner-core tropical feature. A 20/0025Z ASCAT-A
pass indicated a small fetch of mostly straight-flow 40-kt winds
located 60-90 nmi northeast of the well-defined surface center.
Given the distance from the low-level center and lack of any
significant curvature to those winds, undersampling is probably not
occurring. Therefore, the initial intensity is being held at 40 kt
for this advisory, which is consistent with satellite
classifications of T2.5/35 kt from TAFB, SAB, and UW-CIMSS ADT, and
a 19/2202Z SATCON estimate of 42 kt. Epsilon is a large cyclone with
gale-force or tropical-storm-force winds extending outward more than
250 nmi in the northern semicircle.

The initial motion estimate is 360/02 kt. No significant changes
were made to the previous track forecast or reasoning. Epsilon is
expected to meander within weak steering currents well to the
southeast of Bermuda for the next 12 h or so. By late Tuesday, a
ridge is forecast to build to the north and east of the cyclone,
forcing Epsilon generally toward the northwest through Friday. As an
upper-level trough and associated frontal system approach the
cyclone, Epsilon is expected to turn sharply northeastward between
the trough and the ridge by late Friday, and accelerate
northeastward thereafter over over the north Atlantic. The latest
NHC model guidance is coming into better agreement, with a tight
clustering of he various consensus models lying essentially along
the previous advisory track. On the forecast track, Epsilon should
make its closest approach to Bermuda on Friday.

Epsilon is forecast to remain over sea-surface temperatures (SST) of
at least 27C the next 36 h or so and, when coupled with 200-mb
temperatures of -55C, sufficient instability will exist to continue
to allow for deep convection to be generated both in the inner- and
outer-core regions of the cyclone. Thus, gradual strengthening is
forecast during that time. However, by 48 h and continuing through
72 h, SSTs cool to near 26.5C and the depth of the relatively warm
water becomes quite shallow, as indciated by upper-ocean heat
content values dropping to near zero by 72 h. The large and
expansive wind field should result in cold upwelling both ahead of
and beneath the inner-core wind field, which is likely to temper the
intensification process. This may be reflected in the past couple of
HRWF runs which no longer make Epsilon a hurricane by the time the
cyclone approaches Bermuda on Friday. For now, the intensity
forecast has only been lowered slightly since there may be some
baroclinic interaction with an approaching upper-level trough that
could offset the cooler waters. Epsilon could be undergoing
extratropical transition by the 120-h forecast period, but for now
the system will be shown as still being tropical since it will be
located over marginal SSTs near 26C at that time.

Key Message:

1. Epsilon is forecast to be at or near hurricane strength when
it approaches Bermuda late this week. While it is too soon to
determine the exact details of Epsilon's track and intensity near
the island, there is a risk of direct impacts from wind, rainfall,
and storm surge on Bermuda, and interests there should closely
monitor the progress of Epsilon.


FORECAST POSITIONS AND MAX WINDS

INIT 20/0300Z 25.3N 55.3W 40 KT 45 MPH
12H 20/1200Z 26.1N 55.5W 45 KT 50 MPH
24H 21/0000Z 27.5N 56.7W 50 KT 60 MPH
36H 21/1200Z 28.3N 58.5W 55 KT 65 MPH
48H 22/0000Z 29.1N 59.8W 60 KT 70 MPH
60H 22/1200Z 30.4N 60.8W 65 KT 75 MPH
72H 23/0000Z 31.3N 61.5W 70 KT 80 MPH
96H 24/0000Z 32.9N 62.5W 75 KT 85 MPH
120H 25/0000Z 36.4N 60.3W 75 KT 85 MPH
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21-10-2020, 19:46   #248
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Epsilon causing a bit of a stir this evening , from NHC : 'An Air Force Hurricane Hunter aircraft found that Hurricane Epsilon
is significantly stronger than was previously analyzed. A blend of
the flight-level and surface wind data supports an intensity of 95
kt. The intensity forecast has been adjusted upward during the first
12-24 h to account for this new data. It is possible that Epsilon
could strengthen a little more and become a major hurricane later
today before conditions become less conducive tomorrow. '


Set to turn North and a close shave for Bermuda.


NHC

FORECAST POSITIONS AND MAX WINDS

INIT 21/1800Z 29.4N 59.7W 95 KT 110 MPH
12H 22/0000Z 29.6N 60.1W 95 KT 110 MPH
24H 22/1200Z 30.9N 60.8W 90 KT 105 MPH
36H 23/0000Z 32.3N 61.2W 85 KT 100 MPH
48H 23/1200Z 33.7N 61.6W 80 KT 90 MPH
60H 24/0000Z 35.0N 61.6W 80 KT 90 MPH
72H 24/1200Z 36.6N 60.6W 75 KT 85 MPH
96H 25/1200Z 42.0N 51.5W 70 KT 80 MPH
120H 26/1200Z 49.5N 33.0W 65 KT 75 MPH...POST-TROP/EXTRATROP









https://twitter.com/CIRA_CSU/status/...437951488?s=20
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21-10-2020, 23:35   #249
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Epsilon is now a category 3 hurricane. It's funny how this happened not long after GL's post about how major hurricanes tend to form in the Caribbean at this time of year!

Also, I read that this is the only hurricane to intensify by 45+ kts after October 15th, I'm not sure if this is true or not.
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22-10-2020, 09:04   #250
Gaoth Laidir
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Quote:
Originally Posted by Artane2002 View Post
Epsilon is now a category 3 hurricane. It's funny how this happened not long after GL's post about how major hurricanes tend to form in the Caribbean at this time of year!

Also, I read that this is the only hurricane to intensify by 45+ kts after October 15th, I'm not sure if this is true or not.
Yes, that was the map for the satellite era, though of course some major Cat 3+ hurricanes most likely got under-reported due to the lack of aircraft recon data. Epsilon was only upgraded due to aircraft data when all the satellite estimates were much lower.

Here were the NHC's comments yesterday...

Quote:
NWS National Hurricane Center Miami FL AL272020
200 PM AST Wed Oct 21 2020

An Air Force Hurricane Hunter aircraft found that Hurricane Epsilon
is significantly stronger than was previously analyzed. A blend of
the flight-level and surface wind data supports an intensity of 95
kt.

...

An Air Force Hurricane Hunter aircraft that investigated Epsilon earlier
today measured SFMR winds of around 100 kt and max flight level
winds of 100 kt. Dropsonde data indicated peak surface winds of 106
kt with deeper-layer averages of 95-100 kt, which also lends support
to the higher SFMR winds, and surface pressures have fallen since
the special advisory. Therefore the initial intensity is raised to
100 kt, making Epsilon the 4th major hurricane of the season.
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22-10-2020, 13:40   #251
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Apart from the dearth of major hurricanes in the earlier part of the season, the parallels with 2005 continue - storms in 2005 also defied model expectations and forecasting knowledge by strengthening in conditions previously thought to be impossible for strengthening. In 2005, Vince, Delta, Epsilon and Zeta all strengthened in this manner despite SSTs considered too cold for strengthening and high wind shear.

I can't wait for the NHC's post-season analysis of this season next year, it seems obvious to me that there are some as-yet undocumented teleconnections which link both seasons together. The lack of major Cape Verde type hurricanes in July-September is now the only primary difference between the two seasons, and we know what caused this (a combination of a southward displacement of the African jet, an abundance of Saharan dust, and, most unusually, a monsoon trough esque gyre which developed in the East Atlantic during August-September and blocked tropical waves from exiting Africa (thus leaving them moving so slowly once they did reach the Atlantic that they would get sheared to pieces).

Something else is going on in the background this year which is lending storms the ability to strengthen in conditions wherein forecasters and models alike have said "the storm cannot possibly strengthen this much under these conditions". A comparison of the teleconnections with 2005, the other season in which this happened frequently, will be fascinating.

Last edited by hatrickpatrick; 22-10-2020 at 13:43.
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25-10-2020, 22:19   #252
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Tropical Storm Zeta has now been named and it is expected to make landfall in Mexico on Tuesday morning. Is it just me or is the predicted track very similar to Delta's track?
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26-10-2020, 02:18   #253
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Despite the very active season, fewer than 200 deaths to this point, a relatively low total.
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27-10-2020, 20:50   #254
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TS ζ is back out over the southern Gulf of Mexico after crossing the Yucatán peninsula this afternoon. Current intensity is 55 knots. Ocean heat content is much lower than the Caribbean, but still high enough to probably intensify slightly over the next1 12 hours before becoming extratropical by the time it makes landfall in Louisiana in a couple of days.

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28-10-2020, 06:47   #255
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The energy of Zeta (long since becoming extratropical) will possibly be zooming past Ireland on Saturday night.

This is a very fast moving tropical system, not unusual for late in the season. It is interacting with a closed low above Texas and Oklahoma bringing an ice storm to the southern plains states and a rare October snowfall yesterday in New Mexico (5-10" around KABQ). Denver CO has been running 30 deg (F) below normal and I think it has been almost that cold here, but the cold air is going to be trapped over central and northeastern states and not directly contacting the circulation of Zeta, with the polar front around RIC to BNA to MSY and the arctic front parallel but quite a bit further north.

Zeta will zoom in on southeast LA (possibly reaching cat-2 briefly) with a very tight circulation and move quickly through the inland southeast emerging rather bedraggled as just a wave near Ocean City MD, then it redevelops, probably won't be reclassified as a tropical storm but that is how it may be acting briefly when it hits the warmer Gulf stream waters, but whatever happens there, extratropical for sure by Saturday early morning south of Newfoundland and then quickly on to the eastern Atlantic.

The remnants of Zeta will be spread out into multiple waves but one energy centre persists on some model guidance and it could remain intense, with the jet stream compressing later this week. I am mentioning it more as a possibility than a certainty for the weekend forecast but in any case what's left of Zeta will be moving along very quickly at all times from now to its complete dissipation.
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