2018 Hurricane Season

Gaoth Laidir

Florence now 55 knots and set to stay there for the next 24 hours and below hurricane strength for 36-48 hours. Further downgrade in intensity forecast in the latest update.

Meteorite58

Florence experiencing peak wind shear atm. NHC saying moving back into an environment of low shear/ warmer SST's in about 45 hrs allowing for re intensification. Big model spread on strength and track.

Gaoth Laidir

Nearest approach to Bermuda is 240 nautical miles Tuesday evening.

hatrickpatrick

Holy sh!t, if the 6z GFS verifies :eek:

Still FI but inching closer and closer to the reliable timeframe... If we still have charts like this at T-120h, I reckon Florence needs its own dedicated thread. This would be an unbelievable disaster if it played out this way.

gozunda

hatrickpatrick wrote: »

Holy sh!t, if the 6z GFS verifies :eek:

Still FI but inching closer and closer to the reliable timeframe... If we still have charts like this at T-120h, I reckon Florence needs its own dedicated thread. This would be an unbelievable disaster if it played out this way.

Looks like that model is estimating a footfall of that system over Ireland in around the 17th/18th of September or earlier?

Meteorite58

Getting a bit more tense on the E coast as confidence growing of landfall on the SE coast maybe around midweek, possibly Thursday. Messages going out for Hurricane preparedness. Most of the EPS now showing landfall. Exact Track and strength will become refined as the days go on. Not much talk of potential for the track to miss land at this stage.

https://twitter.com/StuOstro/status/1038087516686049285

https://twitter.com/pppapin/status/1038084355417985029

ECM has been fairly consistent with this, more and more looking like the E coast of the US, possibly the Carolina's and looks to be getting very busy with the possibility of 2 or 3 Hurricanes by next week and look where it is sending potential Cyclone 8 just coming off W Africa!

https://twitter.com/MJVentrice/status/1038148630140669959

https://twitter.com/RyanMaue/status/1038150592269639685

Meteorite58

Current GOES 16 Sat Loop. A new area of Disturbance ( trough of LP ) ahead of Florence. Wondering will this affect it's track or possibly have little or no effect ?

Hurricane Hunters to begin flying into Florence Sat Night.










https://twitter.com/EdValleeWx/status/1038153453497982977

sdanseo

Notable that almost all of those intensity guidance models stop at T+120 and almost all of those that stop at that time are on sharply upward trends in terms of windspeed.

Also notable: currently 5 simultaneous areas of interest in the Atlantic / Eastern US if you include Gordon, of which 4 are certain to become cyclones or have already been one.
Another three in the Pacific for 8 in total.

star gazer

Tropical Depression 9 (Isaac) is forecast to become a Tropical Storm and then a Hurricane in the coming days as it travels West towards the Windward Islands.

Tropical Depression 8 (Helene) is 650km East South East of the Cape Verde islands and is due to be a Tropical Storm as it moves through/by. Subsequently it too is forecast to become a Hurricane next week.

Florence should be well South of Bermuda as it passes by with a lot of the models having it make landfall or pass very close to the US East coast. It's due to strengthen again from it's tropical storm status and is forecast to be a Major Hurricane again in about 4 days. It's a good time to check on Hurricane plans for people living on the US East coast.

Gaoth Laidir

sdanseo wrote: »

Notable that almost all of those intensity guidance models stop at T+120 and almost all of those that stop at that time are on sharply upward trends in terms of windspeed.
.

That's been a consistent pattern for the past few days, but on each subsequent update the intensity at each interval comes down, e.g. the last 3 forecast intensities for 18Z on the 9th:

Wednesday's forecast: 105 kt
Thursday's: 90 kt
Tonight's: 70 kt

Similarly other time periods too. The models have not handled things well at all so far, both with intensity and the steering flow. A few days ago the consensus was a northerly turn east of Bermuda.

Here's the 18Z latest SHIPS output, showing an 11-knot drop at 108 hours compared to the 12Z.

http://hurricanes.ral.ucar.edu/realtime/plots/northatlantic/2018/al062018/stext/18090718AL0618_ships.txt

sdanseo

Meteorite58 wrote: »

TD-8 ends up on an interesting trajectory on that run.

Déja vu, anyone?

Gaoth Laidir wrote: »

That's been a consistent pattern for the past few days, but on each subsequent update the intensity at each interval comes down, e.g. the last 3 forecast intensities for 18Z on the 9th:

Wednesday's forecast: 105 kt
Thursday's: 90 kt
Tonight's: 70 kt

Similarly other time periods too. The models have not handled things well at all so far, both with intensity and the steering flow. A few days ago the consensus was a northerly turn east of Bermuda.

Here's the 18Z latest SHIPS output, showing an 11-knot drop at 108 hours compared to the 12Z.

http://hurricanes.ral.ucar.edu/realtime/plots/northatlantic/2018/al062018/stext/18090718AL0618_ships.txt

Probably just as well given the above. :pac:

But I would agree, the models have been all over the place.

Meteorite58

ECM 12Z 850 hPa Wind and MSLP

Early days for exact strength and track and rainfall totals but a closer look here of what the ECM is showing on the latest run. What Florence could look like on some part of the SE coast. All subject to change.

hatrickpatrick

star gazer

Tropical Storm Helene is forecast to strengthen quickly and there's been a Hurricane watch added for some of the Cape Verde islands. nhc

380
WTNT43 KNHC 080850
TCDAT3

Tropical Storm Helene Discussion Number 4
NWS National Hurricane Center Miami FL AL082018
500 AM AST Sat Sep 08 2018

Helene's structure appears to be quickly improving this morning.
The initial intensity has been increased to 40 kt based on a blend
of the latest subjective Dvorak intensity estimates and the
UW-CIMSS SATCON. Several microwave passes overnight indicate that
the cyclone has become more vertically aligned, likely due to a
reformation of the center beneath the strongest convection. In
fact, a 0733 UTC SSMIS image shows the early development of a low-
to mid-level eye, which is often a precursor to intensification.

Nearly all of the intensity guidance seems to have picked up on the
improved structure of Helene, and the models show far more
intensification than before, especially through 48 h. Consequently,
a significant change has been made to the intensity forecast, which
now calls for Helene to become a hurricane on Sunday while it is
near the Cabo Verde islands. Once the cyclone passes the islands,
the environment is expected to remain favorable for intensification
for at least 72 h. By the end of the forecast period, all of the
guidance shows some weakening due primarily to increased shear
associated with an approaching mid- to upper-level trough over the
central Atlantic. Given the recent microwave imagery signature, low
shear, and warm SSTs, its possible that the current forecast is
still too conservative, especially for the first 36 h of the
forecast, and further adjustments could be required if it becomes
clear that Helene is intensifying at a faster rate than expected.

Smoothing through the possible reformation of the center, Helene
appears to be moving west with an initial motion around 275/10 kt.
Little change was required to the track forecast, which has been
nudged only slightly south for the first 48 h of the forecast, in
line with the latest track model consensus. A westward motion
should continue for the next couple of days, as Helene is steered
by a mid-level ridge to the north. By day 5, the aforementioned
trough over the central Atlantic should force Helene to turn toward
the northwest.

FORECAST POSITIONS AND MAX WINDS

INIT 08/0900Z 13.7N 19.6W 40 KT 45 MPH
12H 08/1800Z 13.9N 21.2W 50 KT 60 MPH
24H 09/0600Z 14.1N 23.5W 60 KT 70 MPH
36H 09/1800Z 14.7N 26.3W 70 KT 80 MPH
48H 10/0600Z 15.4N 29.3W 75 KT 85 MPH
72H 11/0600Z 17.2N 35.1W 80 KT 90 MPH
96H 12/0600Z 19.0N 39.5W 70 KT 80 MPH
120H 13/0600Z 22.0N 42.5W 65 KT 75 MPH

$$
Forecaster Zelinsky

Gaoth Laidir

Slight nudge upwards in the latest Florence forecast

BumperD

Isaac will be named later today and is forecast to track west towards the Islands next week. Worth monitoring as it enters the warm waters of the Caribbean

Meteorite58

The ECM OZ shows Helene's path been made easier by a disturbance clearing a path through the Azores HP and showing it at the end of the run join forces with a large area of LP. Could this LP along with the Jet act as a sling shot so to speak sending ex Helene towards us ? A long way off no doubt but will be interesting to watch this develop where ever it ends up. The ECM seems to be doing very well at present. Will be good to look back at this to see how well it performed. If this did come near Ireland it could be 11 or 12 days away.

hatrickpatrick

Aaaaaand we have yet another lemon - the subtropical disturbance I mentioned a few pages back has been added to the NHC. They're only predicting 20% probability of development over five days - if it does develop, which the GFS 12z seems to hint at, it'll likely track due East and impact Spain and Portugal to some extent.

Meteorite58

Latest ECM 12Z has Helene stall around the Azores at +240

Darwin

Good to see the influence of the Azores high potentially helping us out here, hopefully Helene remains a fish storm.

star gazer

Tropical Storm Isaac has developed. It's a serious concern for the Lesser Antilles in five days time. Wind shear is forecast to keep it from developing beyond a Category 1 Hurricane by that time.
nhc

510
WTNT44 KNHC 082048
TCDAT4

Tropical Storm Isaac Discussion Number 5
NWS National Hurricane Center Miami FL AL092018
500 PM AST Sat Sep 08 2018

The structure of the cyclone, while still a shear pattern, is
improving, with the low-level center now near the convective
overcast and improved outflow in the eastern semicircle. Satellite
intensity estimates have increased to the 30-45 kt range, with the
CIMSS satellite consensus technique now suggesting winds near 35
kt. Based on these estimates, the initial intensity is increased to
35 kt and the depression is upgraded to Tropical Storm Isaac.

Isaac is now moving slowly westward, with the initial motion 275/6.
The subtropical ridge to the north of Isaac is forecast to steer the
system westward with an increasing forward speed for at least the
next 2-3 days. After that time, there is some uncertainty in the
track forecast due to the formation of a mid- to upper-level trough
over the central Atlantic, with some of the track guidance showing a
decrease in forward speed and a more northerly motion near the end
of the forecast period. The GFS and ECMWF models show a continued
westerly motion through that time, and the official forecast follows
that scenario, although with a slower forward speed than in the
previous forecast. The new forecast is again similar to the
earlier forecast and lies near the various consensus models.

Conditions appear favorable for gradual strengthening during the
next 72 h as Isaac moves westward across the warm waters of the
tropical Atlantic. In best agreement with the SHIPS model for the
next three days, the new intensity forecast is raised from the
previous forecast during this time. From 72-120 h, the system is
expected to encounter westerly wind shear, which is expected to
cause some weakening.

FORECAST POSITIONS AND MAX WINDS

INIT 08/2100Z 14.5N 36.6W 35 KT 40 MPH
12H 09/0600Z 14.6N 37.7W 40 KT 45 MPH
24H 09/1800Z 14.7N 39.5W 50 KT 60 MPH
36H 10/0600Z 14.7N 42.0W 60 KT 70 MPH
48H 10/1800Z 14.7N 44.6W 65 KT 75 MPH
72H 11/1800Z 14.5N 50.0W 75 KT 85 MPH
96H 12/1800Z 14.5N 55.5W 75 KT 85 MPH
120H 13/1800Z 15.0N 61.0W 70 KT 80 MPH

$$
Forecaster Beven

Gaoth Laidir

Florence's intensity history up to this evening.



Ocean Heat Content over its forecast track for the next 5 days, with values of up to near 40 kJ/cm². That seems a bit low for the rapid intensification being spoken of, but with the shear practically gone it will help. As the storm's speed increases after 48 hours, lower OCH values are needed, but still, values nearer to 100 are normally associated with rapid intensification.



18Z SHIPS output

Rikand

Meteorite58 wrote: »

So Florence is going to make landfall near Florence ?

Meteorite58

star gazer

Hurricane Olivia is due to impact Hawaii in the coming days though it should weaken to a Tropical Storm by then.
Tropical Storm Isaac is due to become a Hurricane and cross a part of the Eastern Caribbean in four to five days.
Tropical Storm Helene is impacting the Cape Verde islands and is forecast to strengthen to a Hurricane.
Guam has issued a Typhoon warning for Mangkhut which after that could become a Super Typhoon.
Tropical Storm Florence is due to strengthen to a Major Hurricane and impact a part of the South Eastern USA.

screamer

Is it possible that any of these could merge or are they too far away from eachother? And if they did, what would be the outcome? I'm no expert at all but looks like Helene is going to be packing some punch there when she gets going....

greedygoblin

Helene has officially achieved hurricane status:
https://twitter.com/NHC_Atlantic/status/1038887781190197248

Rikand

Helene is a long way south and east to be a hurricane already. Its barely clear of the African coast

greedygoblin

screamer wrote: »

Is it possible that any of these could merge or are they too far away from eachother? And if they did, what would be the outcome? I'm no expert at all but looks like Helene is going to be packing some punch there when she gets going....

I'm no expert either but from what I've read they are just that bit too far away from each other to merge. It seems they have to be within a distance of 12 degrees of latitude (~1350 km) for to start having an effect on each other. The process by which they start to interact with one another is known as the Fujiwhara effect.


It seems the Fujiwhara effect played a role in Hurricane Sandy's path over the north-eastern US back in 2012 after it started interacting with an upper-level trough, pulling the hurricane westward towards landfall.

sdanseo

The GFS does absolutely mental things with Florence deep out into FI. Has it stalled over the Carolinas for a few days, then bounces it back out to Bermuda, reintensifies and ends up over Greenland at 937mb by 384h

"Fantasy" Island - the phrase wasn't coined for no reason! Absolutely bananas but funny to look at.