Why?

Crude answer.

Higher latitudes warm faster, jet stream becomes stronger, shear in the tropics gets higher, makes formation more difficult.

 

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Crude answer.

Higher latitudes warm faster, jet stream becomes stronger, shear in the tropics gets higher, makes formation more difficult.

 

But couldn't the extra shear give what we've seen this year, storms starting up (more frequently because of warmer seas) but getting cut off by the shear before they can really develop?

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Crude answer.

Higher latitudes warm faster, jet stream becomes stronger, shear in the tropics gets higher, makes formation more difficult.

 

I did wonder why it is the fact that we are having well above tropical activity/storms but very few hurricanes despite the Tropical Atlantic having well above average SST's.  

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Anyway, this morning there's definitely one to watch in the Caribbean with 60/80% probabilities in  2/5 days of development this week - and a couple of less certain ones out on the Atlantic

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Just looking at this area of disturbance in the central Caribbean sea  - however despite it's 70/80% chance of developing i can't see this appearing on the GFS model runs!? - Or does it need to develop for it to show up on the models!?

 

120 hrs - Looks like there's is little activity

 

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Forecast for development into TS Delta and (by most models)a hurricane approaching New Orleans by Thursday

https://yaleclimateconnections.org/2020/10/tropical-storm-delta-likely-to-form-by-tuesday/ 

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Forecast for development into TS Delta and (by most models)a hurricane approaching New Orleans by Thursday

https://yaleclimateconnections.org/2020/10/tropical-storm-delta-likely-to-form-by-tuesday/ 

Yes here we are - Heading for New Orleans and as a potential Hurricane.

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Delta still south of Jamaica

https://www.star.nesdis.noaa.gov/GOES/floater.php?stormid=AL262020

 

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Growing potential for Delta

 

12z SHIPS text shows virtually little to no shear over #Delta for at least the next 60 hours along with SSTs of around 30C. Unsurprisingly, the rapid intensification probabilities are quite high (>60%) within the next 24 hours. pic.twitter.com/cwitz37Fcn

— Steve Copertino (@TheSteveCop) October 5, 2020

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Pretty substantial tower going up just north of the estimated center of #Delta this morning. Quick strengthening is possible if this is able to rotate around the primitive core of the cyclone. pic.twitter.com/JTaSnMzvkp

— Steve Copertino (@TheSteveCop) October 5, 2020

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Copied from NHC from NOAA:

ZCZC MIATCDAT1 ALL
TTAA00 KNHC DDHHMM

Tropical Storm Delta Discussion Number   4
NWS National Hurricane Center Miami FL       AL262020
1100 AM EDT Mon Oct 05 2020

The convective structure of Delta has continued to improve this 
morning.  Earlier microwave data and early-light visible satellite 
imagery showed that the center of the tropical cyclone re-formed 
farther south within the area of deep convection.  Since that time, 
banding has continued to increase around the southern and eastern 
portion of the circulation, and a small CDO-like feature has formed. 
 The intensity has been set at 40 kt, which is a blend of the 
subjective Dvorak estimate from TAFB and objective satellite 
intensity estimates from UW/CIMSS.  A NOAA Hurricane Hunter aircraft 
is scheduled to investigate the tropical storm this afternoon, which 
should provide a better assessment of the cyclone's intensity, 
structure, and wind field.

With the earlier center re-formation, the initial motion estimate is 
a somewhat uncertain 280/6 kt.  Delta is expected to resume a 
west-northwestward motion later today.  A northwestward heading 
around the southwestern portion of a deep-layer ridge should begin 
tonight or Tuesday, and that general motion with some increase in 
forward speed is expected to continue through 60-72 hours.  After 
that time, a broad mid- to upper-level trough is forecast to develop 
over the south-central United States, which should weaken the 
western portion of the ridge and cause Delta to turn northward 
toward the northern Gulf Coast.  After day 4, Delta should begin to 
accelerate north-northeastward or northeastward ahead of the 
aforementioned trough.  The new NHC track forecast has been adjusted 
to the south and west of the previous advisory during the first 
couple of days, primarily due to the recent center re-formation and 
more southward initial position. After that time, the NHC track is 
not much different than the previous forecast and lies near the 
center of the tightly clustered dynamical model envelope.

Delta is forecast to traverse very warm waters over the northwestern 
Caribbean Sea and be in a very low vertical wind shear environment 
during the next couple of days.  These conditions should allow for 
significant strengthening during that time, and the NHC intensity 
forecast is at or above the various intensity aids.  It is somewhat 
surprising that the intensity aids were generally a little lower 
this cycle, but the expected low shear and SHIPS rapid 
intensification index support the higher than climatological rate 
of intensification.  After 72 hours, increasing southwesterly shear 
and the cooler shelf waters over the northern Gulf are likely to 
induce some weakening later in the period.  The updated NHC 
intensity forecast calls for a faster rate of intensification over 
the next 48-60 hours, but is similar to the previous advisory 
thereafter.

Key Messages:

1. Tropical storm conditions are expected in the Cayman Islands
beginning late today or tonight, and a Tropical Storm Warning is
in effect.

2. Dangerous storm surge and hurricane conditions are expected in 
portions of western Cuba by Tuesday afternoon, and a Hurricane 
Warning is in effect.

3. Heavy rainfall will affect portions of Jamaica, the Cayman 
Islands, and western Cuba during the next few days. This rainfall 
could lead to significant flash flooding and mudslides. 

4. Delta is forecast to approach the northern Gulf Coast late this 
week as a hurricane. While there is large uncertainty in the track 
and intensity forecasts at these time ranges, there is an increasing 
risk of dangerous storm surge, wind, and rainfall hazards along the 
coast from Louisiana to the western Florida Panhandle. Residents in 
these areas should monitor the progress of Delta and check for 
updates to the forecast during the week.

FORECAST POSITIONS AND MAX WINDS

INIT  05/1500Z 16.4N  78.6W   40 KT  45 MPH
 12H  06/0000Z 17.1N  79.6W   50 KT  60 MPH
 24H  06/1200Z 18.7N  81.7W   60 KT  70 MPH
 36H  07/0000Z 20.8N  84.3W   75 KT  85 MPH
 48H  07/1200Z 22.8N  86.8W   85 KT 100 MPH
 60H  08/0000Z 24.6N  89.1W   90 KT 105 MPH
 72H  08/1200Z 26.0N  90.7W   90 KT 105 MPH
 96H  09/1200Z 28.8N  91.1W   85 KT 100 MPH
120H  10/1200Z 33.1N  88.2W   40 KT  45 MPH...INLAND

$$
Forecaster Brown

NNNN

https://www.nhc.noaa.gov/text/refresh/MIATCDAT1+shtml/051453.shtml?

 

---

Copied from NHC from NOAA:

ZCZC MIATCDAT1 ALL
TTAA00 KNHC DDHHMM

Tropical Storm Delta Discussion Number   4
NWS National Hurricane Center Miami FL       AL262020
1100 AM EDT Mon Oct 05 2020

The convective structure of Delta has continued to improve this 
morning.  Earlier microwave data and early-light visible satellite 
imagery showed that the center of the tropical cyclone re-formed 
farther south within the area of deep convection.  Since that time, 
banding has continued to increase around the southern and eastern 
portion of the circulation, and a small CDO-like feature has formed. 
 The intensity has been set at 40 kt, which is a blend of the 
subjective Dvorak estimate from TAFB and objective satellite 
intensity estimates from UW/CIMSS.  A NOAA Hurricane Hunter aircraft 
is scheduled to investigate the tropical storm this afternoon, which 
should provide a better assessment of the cyclone's intensity, 
structure, and wind field.

With the earlier center re-formation, the initial motion estimate is 
a somewhat uncertain 280/6 kt.  Delta is expected to resume a 
west-northwestward motion later today.  A northwestward heading 
around the southwestern portion of a deep-layer ridge should begin 
tonight or Tuesday, and that general motion with some increase in 
forward speed is expected to continue through 60-72 hours.  After 
that time, a broad mid- to upper-level trough is forecast to develop 
over the south-central United States, which should weaken the 
western portion of the ridge and cause Delta to turn northward 
toward the northern Gulf Coast.  After day 4, Delta should begin to 
accelerate north-northeastward or northeastward ahead of the 
aforementioned trough.  The new NHC track forecast has been adjusted 
to the south and west of the previous advisory during the first 
couple of days, primarily due to the recent center re-formation and 
more southward initial position. After that time, the NHC track is 
not much different than the previous forecast and lies near the 
center of the tightly clustered dynamical model envelope.

Delta is forecast to traverse very warm waters over the northwestern 
Caribbean Sea and be in a very low vertical wind shear environment 
during the next couple of days.  These conditions should allow for 
significant strengthening during that time, and the NHC intensity 
forecast is at or above the various intensity aids.  It is somewhat 
surprising that the intensity aids were generally a little lower 
this cycle, but the expected low shear and SHIPS rapid 
intensification index support the higher than climatological rate 
of intensification.  After 72 hours, increasing southwesterly shear 
and the cooler shelf waters over the northern Gulf are likely to 
induce some weakening later in the period.  The updated NHC 
intensity forecast calls for a faster rate of intensification over 
the next 48-60 hours, but is similar to the previous advisory 
thereafter.

Key Messages:

1. Tropical storm conditions are expected in the Cayman Islands
beginning late today or tonight, and a Tropical Storm Warning is
in effect.

2. Dangerous storm surge and hurricane conditions are expected in 
portions of western Cuba by Tuesday afternoon, and a Hurricane 
Warning is in effect.

3. Heavy rainfall will affect portions of Jamaica, the Cayman 
Islands, and western Cuba during the next few days. This rainfall 
could lead to significant flash flooding and mudslides. 

4. Delta is forecast to approach the northern Gulf Coast late this 
week as a hurricane. While there is large uncertainty in the track 
and intensity forecasts at these time ranges, there is an increasing 
risk of dangerous storm surge, wind, and rainfall hazards along the 
coast from Louisiana to the western Florida Panhandle. Residents in 
these areas should monitor the progress of Delta and check for 
updates to the forecast during the week.

FORECAST POSITIONS AND MAX WINDS

INIT  05/1500Z 16.4N  78.6W   40 KT  45 MPH
 12H  06/0000Z 17.1N  79.6W   50 KT  60 MPH
 24H  06/1200Z 18.7N  81.7W   60 KT  70 MPH
 36H  07/0000Z 20.8N  84.3W   75 KT  85 MPH
 48H  07/1200Z 22.8N  86.8W   85 KT 100 MPH
 60H  08/0000Z 24.6N  89.1W   90 KT 105 MPH
 72H  08/1200Z 26.0N  90.7W   90 KT 105 MPH
 96H  09/1200Z 28.8N  91.1W   85 KT 100 MPH
120H  10/1200Z 33.1N  88.2W   40 KT  45 MPH...INLAND

$$
Forecaster Brown

NNNN

https://www.nhc.noaa.gov/text/refresh/MIATCDAT1+shtml/051453.shtml?

 

If it's forecast to be 45mph at landfall or inland then surely it's not much cause for concern!? 

---

Instead of a long and verbose summay, look at 
https://www.nhc.noaa.gov/refresh/graphics_at1+shtml/174744.shtml?cone#contents
which shows landfall as a hurricane >74mph.

Review on 
https://yaleclimateconnections.org/2020/10/tropical-storm-delta-forms-in-the-caribbean/ 
with charts and this quote
Delta could be anywhere between a strong tropical storm and a category 3 hurricane at landfall in the U.S., with the official NHC forecast of a category 2 hurricane with 100 mph winds a reasonable prediction.

---

Gamma only barely looks like a TC to me. The deep convection is thousands of miles to the north of the low level centre. Should be declassified by tommorow as a remenant low.

 

---

Delta looks to be on a rapid intensification cycle. I suspect estimates of strength as the storm approaches the Gulf Coast will need to be revised upward.
Also don’t rule out some form of interaction with the remnants of Gamma.

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Delta now a hurricane and likely to become a major hurricane as it approaches the yucatan - cancun looks to be in the firingline.

Delta looks to be on a rapid intensification cycle. I suspect estimates of strength as the storm approaches the Gulf Coast will need to be revised upward.
Also don’t rule out some form of interaction with the remnants of Gamma.

Intensity forecasts keep getting revised upward - a bad sign.

---

 

Intensity forecasts keep getting revised upward - a bad sign.

The only thing that will save the Gulf Coast from the effects of impact by a major Cat 3/4 hurricane is the cooler strip of shallower water in the northern Gulf. Wind shear tend to be less of an influence with big storms so the 20-25mph shear is unlikely to have an effect.

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The only thing that will save the Gulf Coast from the effects of impact by a major Cat 3/4 hurricane is the cooler strip of shallower water in the northern Gulf. Wind shear tend to be less of an influence with big storms so the 20-25mph shear is unlikely to have an effect.

Yes I looked at the SST's in the Gulf - how come it's 72'F of 21c off the northern Gulf of Mexico - it's some 10c cooler than other parts? is it because of colder weather or previous storms?

---

 

But couldn't the extra shear give what we've seen this year, storms starting up (more frequently because of warmer seas) but getting cut off by the shear before they can really develop?

That's an interesting take and plausible.

The counterargument is that stronger storms are more shear resistant although that only really kicks in by the time you get to major status.

 

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