SEPTEMBER 2018 - Very Wet Month Wrap Up

[don]

Looks like a Flash Flood Watch may be needed for Monday, and it also looks like they are siding with the Euro for now...

Area Forecast Discussion
National Weather Service Houston/Galveston TX
348 PM CDT Sat Sep 1 2018

.DISCUSSION...
Subsidence was stronger than anticipated late this morning and
early this afternoon but now storms begging to fire up along the
seabreeze. Expect scattered showers and thunderstorms to develop
and expand slowly northwestward the remainder of the afternoon.
Brief heavy downpours possible along with lightning threat through
early evening. Plume of deep tropical moisture 2.2-2.4" PW over
the northwest Gulf should spread into the region Sunday afternoon.
So expect a lull late evening in convection with skies clearing
somewhat tonight. Then after midnight storms redevelop over the
Gulf and spread into the coast in the morning hours...expanding
inland in the afternoon. Heavy rainfall threat should increase
Sunday afternoon. This moisture will stall over the region Monday
and as upper levels become more favorable (and possibly some weak
low level circulations forming in the Gulf) will see a window
Sunday night through Monday evening for more heavy downpours with
scattered to numerous storms. At this point it looks like the
areas from Edna to Conroe to Groveton southeastward to greatest
threat near the coast. Confidence increasing for a flash flood
watch being needed Monday.


Tuesday through Thursday could see something of lull in the
intensity of rainfall over SETX with slightly drier air spreading
in late Tuesday. But the area of disturbed weather over the
Bahamas will be moving northwest and could be moving into the
warm eastern Gulf with the potential for development.

Friday and beyond...this tropical disturbance (NHC-40 percenter
for development) could turn more westward. Have favored the ECMWF
solution which paints a much wetter solutions over SETX as the
system behaves as a brown water inland development/organization
system over LA/SETX (tap of 2.2-2.5" PW feeding it from the Gulf)
...drifting slowly westward bringing copious rainfall to the
region over a 3+ day period. Stay tuned we are nearing the
climatological peak of hurricane season.


Oh yeah temps...rainfall/increased cloud cover should help to
hold down temperatures during the day and up over night this week.
45

[unome]

OPC's Atlantic surface charts show "possible tropical cyclone" on 72 & 96 hr forecasts, currently & NHC's 72 hr marine forecast chart does not ?

https://ocean.weather.gov/Atl_tab.shtml
https://www.nhc.noaa.gov/marine/

I thought the OPC was supposed to defer to NHC ?

[Andrew]

I talked to 3 pros met they said throw the gfs out it’s been clueless

It's not useless, and people who say just throw out a dynamical global model like the GFS because the ECMWF is statistically a better model are not helping anyone. In fact, it is usually the second most reliable model that we have available to track tropical storms.

[stormlover]

Ukmet is better

[Andrew]

Ukmet is better

Both models have their weakness and strengths. UKMET has improved over the last couple years and from a verification perspective they are very similar.

Edit to add, with that said the UKMET is currently an outlier for track during up to landfall. It is currently grouped with the CMC which usually performs the worst. It also keeps it weak until it enters the gulf where marginal development occurs.

[Cpv17]

UKMET and GFS are both pretty good for tracking the tropics most of the time.

[Andrew]

18GFS is showing a tropical storm going into SE Louisiana and does show a lot more favorable environment from Tuesday morning into Wednesday morning. I do believe that is where the best chance for intensification is to occur. All models also indicate this storm will remain small so if environmental conditions remain favorable it won't take long to ramp up.

gfs_ow850_seus_15.png

gfs_ow850_seus_21.png

[Cpv17]

18z GFS has no threat to Texas with this system. Euro has a major threat. Which one to believe? Another classic GFS vs Euro battle.

[jasons2k]

I just don’t see this system busting right through a strengthening ridge like that. Most likely Euro FTW, again..

[srainhoutx]

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT SAT SEP 1 2018

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO:

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM FLORENCE, LOCATED ABOUT A FEW HUNDRED MILES WEST OF THE
CABO VERDE ISLANDS.

DISORGANIZED SHOWERS AND THUNDERSTORMS OVER THE SOUTHEASTERN AND
CENTRAL BAHAMAS, THE TURKS AND CAICOS ISLANDS, AND ADJACENT
ATLANTIC WATERS ARE ASSOCIATED WITH A TROPICAL WAVE AND AN
UPPER-LEVEL TROUGH. THIS ACTIVITY IS EXPECTED TO MOVE
WEST-NORTHWESTWARD ACROSS THE REMAINDER OF THE BAHAMAS AND SOUTH
FLORIDA DURING THE NEXT DAY OR SO AND LITTLE, IF ANY, DEVELOPMENT
IS EXPECTED DURING THAT TIME DUE TO STRONG UPPER-LEVEL WINDS.
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BECOME A LITTLE MORE
FAVORABLE FOR DEVELOPMENT WHEN THE SYSTEM MOVES ACROSS THE GULF OF
MEXICO, WHERE A TROPICAL DEPRESSION COULD FORM DURING THE EARLY TO
MIDDLE PART OF NEXT WEEK. REGARDLESS OF DEVELOPMENT, HEAVY RAINS
ARE LIKELY ACROSS MUCH OF THE BAHAMAS AND SOUTHERN FLORIDA DURING
THE NEXT DAY OR TWO. SEE PRODUCTS FROM YOUR LOCAL WEATHER FORECAST
OFFICE FOR MORE INFORMATION.
* FORMATION CHANCE THROUGH 48 HOURS...LOW...20 PERCENT.
* FORMATION CHANCE THROUGH 5 DAYS...MEDIUM...50 PERCENT.

$$
FORECASTER CANGIALOSI

[Cpv17]

I just don’t see this system busting right through a strengthening ridge like that. Most likely Euro FTW, again..

That’s the same thing that I’m thinking. There will be a strong ridge dropping down SE out of Canada into the N. Plains trying to link up with the east coast ridge. There may be a chance for the system to escape by splitting in between the two ridges which is what the GFS sees, but the Euro just makes more sense by sending it to the west and southwest away from the ridging.

[unome]

Excessive Rainfall Forecast https://www.wpc.ncep.noaa.gov/qpf/ero.p ... curr&day=3

snippet from Day 3

...Portions of the Upper Texas coast into Southwest Louisiana...
As the mid-level circulations weakens and becomes absorbed by the
deep south southwest flow on the back side of the mid-level ridge
over the East Coast, the tropical moisture associated is expected
to feed convection over the Upper Texas coast into southwest
Louisiana. Instability could end up being the limiting factor for
a more widespread flash flood threat, but warm rain processes
dominating the convection could result in hourly rainfall rates in
excess of 2.00 inches. Three hour flash flood guidance values are
as as low as 2.00/2.50 inches, so a low end flash flood threat
still remains, especially in urban areas such as Houston. Based on
this, a Marginal Risk was placed here for Day 3.

[sau27]

I noticed the "brown ocean" effect the Euro was seeing the past couple of runs and thought it was interesting that it was seeing something like that so far out. I find it a little suprising that HGX is putting enough stock in that solution to specifically mention it in their AFD.

[Andrew]

GFS keeping the wave weak through 54 hours. Could be until the last 24 hours before an actual surface low develops.

Looking at it further, the GFS is really weak in this one run as it remains decoupled. 850v and 500v are not stacked at all and it shows it in the intensity.

Trough over the central plains is also a little stronger on this run too so no stalling and southwest push will occur.

H54:

gfs_z850_vort_seus_10.png

H66:

gfs_z850_vort_seus_12.png

H78:

gfs_z850_vort_seus_14.png

[Andrew]

FWIW The CMC is also trending east and not stalling over the region.

gem_z850_vort_seus_14.png

gem_z850_vort_seus_19.png

[stormlover]

0z UKMET looks quite similar in track to the past 2 runs of the Euro.

[stormlover]

Germany icon model like the euro also

[Andrew]

Germany icon model like the euro also

That model is on comparison to the CMC and NAM FWIW.

Edit to add UKMET track

NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 66 HOURS
FORECAST POSITION AT T+ 66 : 27.6N 88.6W

LEAD CENTRAL MAXIMUM WIND
VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS)
-------------- ---- -------- ------------- -------------
0000UTC 05.09.2018 72 28.2N 89.3W 1007 35
1200UTC 05.09.2018 84 29.4N 90.5W 1004 38
0000UTC 06.09.2018 96 30.3N 91.4W 1001 32
1200UTC 06.09.2018 108 30.6N 92.8W 1000 28
0000UTC 07.09.2018 120 30.3N 94.2W 1000 28
1200UTC 07.09.2018 132 29.6N 95.4W 998 36
0000UTC 08.09.2018 144 28.9N 96.3W 997 41

[stormlover]

Not the ukmet though

[Andrew]

Not the ukmet though

wasn't talking about that one.