SEPTEMBER 2018 - Very Wet Month Wrap Up

[unome]

happy for you, Jason

looks like a slab of precip might hit a good portion of us !

[Katdaddy]

The evening satellite image looks quite impressive over the NW GOM just offshore of TX and LA.

[Rip76]

Wow.

[djmike]

WOW Kat! If i didnt know any better this system over us right now looks like a decent hurricane. Any chance it may strengthen a tad before fully onshore? I know no winds but its gotta be soaking up a ton of moisture. Im getting a little concerned bere in Beaumont as a met here said a possibility of 7-8” before this moves out Monday evening...

[unome]

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
605 PM EDT Sun Sep 02 2018

Day 1
Valid 2205Z Sun Sep 02 2018 - 12Z Mon Sep 03 2018

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER THE MIDDLE
MISSISSIPPI VALLEY...
...THERE IS NOW A SLIGHT RISK OF EXCESSIVE RAINFALL OVER SOUTH
FLORIDA...

...Central Plains into the Mid MS Valley and Great Lakes...
Additional convection will occur across IA into southern WI and
northern IL this afternoon and overnight. Like the synoptic
situation, the high res model signal is not quite as robust over
the area today compared to recent days...but we still expect an
additional 1-3"...and still the potential for localized 3-5"
totals given the persistent (albeit weaker) moisture transport
supportive of some training/backbuilding and higher PWs. Given the
heavy antecedent rainfall over central and southern IA, this
additional rainfall likely poses an elevated flash flood threat,
and hence a Moderate Risk of excessive rainfall for much of
southern and central IA.

The heaviest rainfall magnitudes over the Day 1 period may
actually end up falling farther south across central KS into far
southeast NE. 850mb moisture transport is more impressive across
this corridor...and the persistent and stationary nature of this
moisture transport axis is very favorable for backbuilding and
training convection. Thus would appear like a corridor of longer
duration heavy rains is possible, with numerous hi-res model
solutions depicting pockets of 5"+ totals. Current indications are
that this activity should end up mainly south of where the
heaviest antecedent rainfall has been. For this reason we will
keep the risk level at Slight across KS and southeast NE, but will
need to monitor closely.

...Texas and Louisiana Coast...
Recent HRRR runs were becoming increasingly suggestive of focused
heavy rainfall that may occur overnight near the mid-level pseudo
warm core circulation that was drifting onto the Gulf Coast. Last
night more than 5 inches of rain fell over a small part of the
Louisiana coast. In similar fashion, a small area from Houston to
Beaumont to Lake Charles, especially centered near Beaumont, could
experience local 5-plus inch amounts tonight. For now, we will
maintain Slight Risk across the region, but as confidence builds,
a local upgrade to Moderate Risk is not out of the question.

...South Florida...
The National Hurricane Center designated Potential Tropical
Cyclone Seven over the Bahamas, initiating advisories at 21Z.
Model forecasts of future rainfall over parts of Florida had
increased during the daytime model cycle. A familiar pattern for
heavy rainfall production will move into place by early Monday as
the tropical wave and perhaps an embedded low pressure center move
over the south peninsula and the Keys. In addition to tropical
downpours from convergence and deepening of the wave, we will see
stronger and deeper east to southeasterly flow fill in across
particularly the south Florida peninsula during the day. This
pattern typically provides a steady supply of instability over the
land areas so that the fuel for convection is not exhausted nor
dependent on the diurnal heating cycle. Additionally, Corfidi
vectors for backward propagation based on the GFS suggest
organized convective clusters will propagate slowly back into the
inflow, toward the east or southeast at zero to ten knots. This
sets up the potential for prolonged heavy rain at a given
location. While the areal average rainfall through the event may
only be 2 to 4 inches based on quick movement of the overall
system, these mesoscale influences could lead to much heavier
local rainfall events, including near the populated areas of
southeast Florida and the upper Keys. Several hi-res models,
particularly the NAM CONUS Nest, and WRF-ARW, indicate some
higher-end rainfall amounts above 5 or 6 inches to occur on
Monday. The event is likely to begin late Sunday night, and in
coordination with WFO Miami and Key West, we are upgrading parts
of south Florida to a Slight Risk of excessive rainfall for the
late night period leading into Day 2.

...Southwest...
Isolated to scattered convective activity expected again today.
Across AZ PWs are not as high as would like to see them for a more
organized flash flood threat. Although deep layer shear and
forcing are both again strong enough to pose at least some threat
of activity organized enough to pose a localized flash flood risk.

Moisture is a bit better from eastern NM into west TX...although
generally not expecting much organization to convection...which
should keep the flooding threat in the Marginal category.

Burke


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt

[unome]

Levi Cowan of Tropical Tidbits posted an update a few hours ago

https://twitter.com/TropicalTidbits/sta ... 2842710017

https://www.tropicaltidbits.com/blog/20 ... ulf-coast/

[ticka1]

what happened to all the rain?

[Rip76]

Possibly after midnight.

[Andrew]

Both the HRRR and Tx-Tech WRF indicate that most of the precipitation may form along the coastline tonight. Obviously, with these type of systems they are hard to predict where precipitation sets up until it actually does, but it is a scenario that often happens. I hope that isn't the case because central part of the region could be dry slotted.

With that said, there does seem to be a couple of boundaries over central SE Texas that we will have to monitor overnight. 925mb-850mb moisture advection is still a lot stronger east of here and that is where PWATs >2.5 are located. This will progress to the northwest overnight into tomorrow. That will be when we really have to monitor for development. Overall, I suspect the coastal counties will have the highest chance of rain with a gradual decrease the more north and west you go.

[jasons2k]

I have a feeling when this week is all said and done, I will have a lot less rain than what the models were showing on yesterday...I’ll be lucky to get 3 or 4”, if that...

[Rip76]

Wow, did the the atmosphere get worked over that bad this morning?

I figured something would fire by 10pm.

[Ptarmigan]

The evening satellite image looks quite impressive over the NW GOM just offshore of TX and LA.

Quite impressive on satellite. Looks like a hurricane.

[Cpv17]

I have a feeling when this week is all said and done, I will have a lot less rain than what the models were showing on yesterday...I’ll be lucky to get 3 or 4”, if that...

Completely agree with you.

[jasons2k]

So far I’m at 1.14”. - I’ll take that!

[Cpv17]

So far I’m at 1.14”. - I’ll take that!

So in the past 3 days here we’ve had a 30% chance of rain, 40%, & 60% today. Guess which day we got rain? Friday, when we had our lowest chance lol we got nothing here the past couple days, but picked up 1.8” Friday afternoon. It’s funny how that works out sometimes. We actually ended up receiving 3.4” altogether this past week so I really don’t have anything to complain about, but I’d love another 3.4” this week

[Andrew]

Wow, did the the atmosphere get worked over that bad this morning?

I figured something would fire by 10pm.

Most models were pretty aggressive with bands forming during the early morning and that still looks on track as better moisture advection begins to take place here over the next several hours. I do suspect that the largest outbreak of convection will be along the coastline though. Hopefully we can get some of that scattered north.

[Cpv17]

Wow, did the the atmosphere get worked over that bad this morning?

I figured something would fire by 10pm.

Most models were pretty aggressive with bands forming during the early morning and that still looks on track as better moisture advection begins to take place here over the next several hours. I do suspect that the largest outbreak of convection will be along the coastline though. Hopefully we can get some of that scattered north.

I looked at the NAM, RGEM, & GFS models a few minutes ago for my area (Wharton County) and none of them have much for my area the next couple days with these high rain chances. Best chance for rain appears to be along the coast and east of 45.

[Andrew]

Wow, did the the atmosphere get worked over that bad this morning?

I figured something would fire by 10pm.

Most models were pretty aggressive with bands forming during the early morning and that still looks on track as better moisture advection begins to take place here over the next several hours. I do suspect that the largest outbreak of convection will be along the coastline though. Hopefully we can get some of that scattered north.

I looked at the NAM, RGEM, & GFS models a few minutes ago for my area (Wharton County) and none of them have much for my area the next couple days with these high rain chances. Best chance for rain appears to be along the coast and east of 45.

Most of the convection is going to be scattered and is hard to properly initialize at such a small scale. That is why global models like the GFS usually have a hard time accurately displaying it. With these type of setups, I depend on the HRRR and Tx-tech wrf because they usually have the resolution to give a more accurate idea. Even then though sometimes you just have to wait until banding actually sets up. Over the next week, I do think most everyone will see 1-3 inches.

[DoctorMu]

Whew! Dont need too much rain from 7. An eastern landfall woul be best for us but bad for them. Any chance it continues an eastern shift or a more western shift? Thoughts? I though the high was supposed to block it from going nortward and send more on a western track. Ensembles still show a southern Louisiana into setx. Track is now eastern Louisiana into northern Louisiana and onward north. Im confused.

I think the current track is going to verify pretty nicely. A lot of the models that were showing a strong west shift have adjusted further east. For instance, the ECMWF ensembles for the most part shifted a good bit east with a less west bend after landfall. .

The GFS was ahead of the game if that scenario holds. Who’d a thunk it?

[djmike]

Beaumont is flooded... 7” so far and counting. This sustem has just begun. Im stranded along with my neighbors in my neighborhood cause no one can get out.