All rather unexpected, NHC developement probabilities dropping from 30%
to 10% over the last few days and going away from Trumpland. Can
anything be read into
"Tropical cyclone formation is not expected for the next 5 days"
rather than "Tropical cyclone formation is not expected".?
GFS seems to have the parcel of tropical air being absorbed and
dissipated by the Azores High over the next few days, is my reading of
its track. SST all rather average in that area.


--
Monthly public talks on science topics, Hampshire , England
http://diverse.4mg.com/scicaf.htm

On Wednesday, 21 August 2019 08:24:33 UTC+1, N_Cook wrote:
All rather unexpected, NHC developement probabilities dropping from 30%
to 10% over the last few days and going away from Trumpland. Can
anything be read into
"Tropical cyclone formation is not expected for the next 5 days"
rather than "Tropical cyclone formation is not expected".?
GFS seems to have the parcel of tropical air being absorbed and
dissipated by the Azores High over the next few days, is my reading of
its track. SST all rather average in that area.

It's the wind shear in that area that is suppressing formation. This is down to the remnant effects of the dissipating El Nino (sea temps may not be indicative of El Nino, but the atmosphere is still "re-adjusting" to the neutral state. Models are struggling with this, but indicate that it will continue. We should see a surge in activity in September once this has progressed.

--
Freddie
Dorrington
Shropshire
115m AMSL
http://www.hosiene.co.uk/weather/
Stats for the month so far: https://www.hosiene.co.uk/weather/st...cs/latest.xlsx

On 21/08/2019 08:24, N_Cook wrote:
All rather unexpected, NHC developement probabilities dropping from 30%
to 10% over the last few days and going away from Trumpland. Can
anything be read into
"Tropical cyclone formation is not expected for the next 5 days"
rather than "Tropical cyclone formation is not expected".?
GFS seems to have the parcel of tropical air being absorbed and
dissipated by the Azores High over the next few days, is my reading of
its track. SST all rather average in that area.



Chantal look to be right on the boundary of colder-than-average water to
the north and warmer to the south.

Here's the latest forecast discussion:


000
WTNT44 KNHC 210835
TCDAT4

Tropical Storm Chantal Discussion Number 2
NWS National Hurricane Center Miami FL AL042019
500 AM AST Wed Aug 21 2019

Chantal has changed little overnight. A small area of deep
convection has persisted northeast of the tropical storm's exposed
surface center. Given the steady-state structure of the cyclone, the
initial intensity has been held at 35 kt based on earlier ASCAT
data.

Only minor adjustments were made to the NHC track and intensity
forecasts, the most substantial of which is that Chantal is now
expected to become a remnant low within 96 h. The tropical storm is
surrounded by dry air and will be moving over marginal SSTs for the
next couple of days. As a result of this unfavorable environment,
Chantal is expected to weaken to a tropical depression by 48 h. Most
of the dynamical models indicate that the cyclone will lose all of
its convection and become post-tropical soon after, but the official
forecast conservatively maintains the system as a tropical cyclone
for 72 h. The official intensity forecast is near a consensus of the
GFS, HMON, and HWRF models.

The tropical storm is moving quickly eastward, but is forecast to
slow and turn southeastward by Thursday. It should then turn toward
the south on Friday as it moves around the northeast periphery of a
low- to mid-level ridge centered over the central Atlantic. The
track guidance is in good agreement on the forecast, at least as
long as Chantal remains a tropical cyclone. The uncertainty in the
track forecast is higher after the cyclone becomes a remnant low,
but most of the guidance generally suggests that Chantal will become
trapped in weak steering flow and meander over the North Atlantic
for a couple days thereafter.

FORECAST POSITIONS AND MAX WINDS

INIT 21/0900Z 40.3N 53.7W 35 KT 40 MPH
12H 21/1800Z 40.2N 50.4W 35 KT 40 MPH
24H 22/0600Z 39.6N 46.3W 35 KT 40 MPH
36H 22/1800Z 38.4N 43.4W 35 KT 40 MPH
48H 23/0600Z 37.2N 42.0W 30 KT 35 MPH
72H 24/0600Z 35.3N 42.4W 30 KT 35 MPH
96H 25/0600Z 35.5N 44.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 26/0600Z 37.5N 44.0W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Zelinsky

--
Graham P Davis, Bracknell, Berks. Web-site: http://www.scarlet-jade.com/
“Understanding is a three-edged sword. Your side, my side, and the
truth.� [Ambassador Kosh]
Posted via Mozilla Thunderbird on openSUSE Tumbleweed.

On 21/08/2019 09:38, Freddie wrote:
On Wednesday, 21 August 2019 08:24:33 UTC+1, N_Cook wrote:
All rather unexpected, NHC developement probabilities dropping from 30%
to 10% over the last few days and going away from Trumpland. Can
anything be read into
"Tropical cyclone formation is not expected for the next 5 days"
rather than "Tropical cyclone formation is not expected".?
GFS seems to have the parcel of tropical air being absorbed and
dissipated by the Azores High over the next few days, is my reading of
its track. SST all rather average in that area.

It's the wind shear in that area that is suppressing formation. This is down to the remnant effects of the dissipating El Nino (sea temps may not be indicative of El Nino, but the atmosphere is still "re-adjusting" to the neutral state. Models are struggling with this, but indicate that it will continue. We should see a surge in activity in September once this has progressed.


FWIW my colour-bin pixel-counting of NOAA El Nino sea-area public-access
3.4 SST anomaly plots. Perhaps the correction was too abrupt and
negative forcing is kicking-in back to El Nina.

To simple visual inspection, more "red" in the sea-area next eastwards
to "3.4" compared to earlier, and any warming tends to progress
westwards it seems as well as slowing of the drop to neutral.
2019 day-number: deg C SSt anomaly
178:Nino +0.60
182 : nino +0.68
185 : Nino +0.83
189: Nino +0.81
192: Nino +0.77
196 : Nino +0.76
199 : Nino +0.67
203 : Nino +0.68
206: Nino +0.64
210 (29 July 2019): Nino +0.52
213: Nino +0.48
217:Nino +0.40
220: Nino +0.38
227 (15 Aug 2019): Nino +0.19
231: Nino +0.17

--
Monthly public talks on science topics, Hampshire , England
http://diverse.4mg.com/scicaf.htm

On 21/08/2019 12:16, Graham P Davis wrote:
On 21/08/2019 08:24, N_Cook wrote:
All rather unexpected, NHC developement probabilities dropping from
30% to 10% over the last few days and going away from Trumpland. Can
anything be read into
"Tropical cyclone formation is not expected for the next 5 days"
rather than "Tropical cyclone formation is not expected".?
GFS seems to have the parcel of tropical air being absorbed and
dissipated by the Azores High over the next few days, is my reading of
its track. SST all rather average in that area.



Chantal look to be right on the boundary of colder-than-average water to
the north and warmer to the south.

Here's the latest forecast discussion:


000
WTNT44 KNHC 210835
TCDAT4

Tropical Storm Chantal Discussion Number 2
NWS National Hurricane Center Miami FL AL042019
500 AM AST Wed Aug 21 2019

Chantal has changed little overnight. A small area of deep
convection has persisted northeast of the tropical storm's exposed
surface center. Given the steady-state structure of the cyclone, the
initial intensity has been held at 35 kt based on earlier ASCAT
data.

Only minor adjustments were made to the NHC track and intensity
forecasts, the most substantial of which is that Chantal is now
expected to become a remnant low within 96 h. The tropical storm is
surrounded by dry air and will be moving over marginal SSTs for the
next couple of days. As a result of this unfavorable environment,
Chantal is expected to weaken to a tropical depression by 48 h. Most
of the dynamical models indicate that the cyclone will lose all of
its convection and become post-tropical soon after, but the official
forecast conservatively maintains the system as a tropical cyclone
for 72 h. The official intensity forecast is near a consensus of the
GFS, HMON, and HWRF models.

The tropical storm is moving quickly eastward, but is forecast to
slow and turn southeastward by Thursday. It should then turn toward
the south on Friday as it moves around the northeast periphery of a
low- to mid-level ridge centered over the central Atlantic. The
track guidance is in good agreement on the forecast, at least as
long as Chantal remains a tropical cyclone. The uncertainty in the
track forecast is higher after the cyclone becomes a remnant low,
but most of the guidance generally suggests that Chantal will become
trapped in weak steering flow and meander over the North Atlantic
for a couple days thereafter.

FORECAST POSITIONS AND MAX WINDS

INIT 21/0900Z 40.3N 53.7W 35 KT 40 MPH
12H 21/1800Z 40.2N 50.4W 35 KT 40 MPH
24H 22/0600Z 39.6N 46.3W 35 KT 40 MPH
36H 22/1800Z 38.4N 43.4W 35 KT 40 MPH
48H 23/0600Z 37.2N 42.0W 30 KT 35 MPH
72H 24/0600Z 35.3N 42.4W 30 KT 35 MPH
96H 25/0600Z 35.5N 44.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 26/0600Z 37.5N 44.0W 30 KT 35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Zelinsky


I see Chantal has appeared on MetO synoptic charts outputted today,
presumably disappearing south off the bottom after 60 hours out.


--
Monthly public talks on science topics, Hampshire , England
http://diverse.4mg.com/scicaf.htm

I like the NHC request, presumably because the clouds mask the
satellites, for them to go back to old tech and
"REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 40.2N 51.6W"



--
Monthly public talks on science topics, Hampshire , England
http://diverse.4mg.com/scicaf.htm

N_Cook wrote:

I like the NHC request, presumably because the clouds mask the
satellites, for them to go back to old tech and "REQUEST FOR 3 HOURLY
SHIP REPORTS WITHIN 300 MILES OF 40.2N 51.6W"

That's a standard request. Nothing like a bit of ground truth!

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
https://peakdistrictweather.org
twitter: @TideswellWeathr

On 21/08/2019 13:31, N_Cook wrote:
To simple visual inspection, more "red" in the sea-area next eastwards
to "3.4" compared to earlier, and any warming tends to progress
westwards it seems as well as slowing of the drop to neutral.
2019 day-number: deg C SSt anomaly
178:Nino +0.60
182 : nino +0.68
185 : Nino +0.83
189: Nino +0.81
192: Nino +0.77
196 : Nino +0.76
199 : Nino +0.67
203 : Nino +0.68
206: Nino +0.64
210 (29 July 2019): Nino +0.52
213: Nino +0.48
217:Nino +0.40
220: Nino +0.38
227 (15 Aug 2019): Nino +0.19
231: Nino +0.17

El Nino may be on the ascendant again, latest pixel counting
234: Nino +0.20

--
Monthly public talks on science topics, Hampshire , England
http://diverse.4mg.com/scicaf.htm