ATL: GRACE - Renmants - Discussion

[crownweather]

Just curious, does anyone know if there have been storms in the past where the models never developed the storm, but it became a hurricane? I know there's probably nothing documented, but wondering if anyone has ever seen that before?

Yep, I distinctly remember Hurricanes Dean and Felix from 2007 that were both forecast by the GFS model to be barely a low pressure system as it tracked across the Caribbean. Both ended up being major hurricanes.

[gatorcane]

Even Danny from a few weeks ago could be considered as all models (except the UKMET) showed dissipation in their medium range forecasts but Danny became a major hurricane. I remember how the ECMWF went from literally nothing to something in one run and it was in the medium-range too. The UKMET, however, was very bullish with Danny from the beginning so that is why I am paying attention to the UKMET this time - it is not dissipating Grace within 5 days like the ECMWF is.

[gatorcane]

000
WTNT42 KNHC 062041
TCDAT2

TROPICAL STORM GRACE DISCUSSION NUMBER 6
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072015
500 PM AST SUN SEP 06 2015

Grace is a fairly well-organized, compact tropical cyclone with
banding features and well-defined upper-level outflow to the north
and south of the system. Deep convection has been rather limited
today, but recent imagery shows some cold cloud tops developing near
the center. The current intensity is set to 45 kt in agreement with
a subjective Dvorak estimate from TAFB. Since the vertical wind
shear is expected to remain modest for the next 24 hours or so,
there is window of opportunity for short-term strengthening. Within
36 hours, the dynamical guidance shows the shear increasing to over
20 kt, and this should cause a weakening trend beginning around that
time. The official intensity forecast is a little above the model
consensus for the first half of the period and close to, or a little
below, the consensus thereafter. It is worth noting that the GFS
shows significant weakening of the cyclone in 4 to 5 days, with the
ECMWF showing dissipation by that time.

The storm has accelerated a bit and is now moving at about 280/13.
For the next several days, Grace should continue to move within a
moderate low- to mid-level easterly flow on the south side of the
subtropical ridge. The track guidance models are noticeably faster
than they were on the previous cycle, so the official forecast is
adjusted accordingly. The NHC track is not far from the latest
dynamical model consensus, TVCN.

FORECAST POSITIONS AND MAX WINDS

INIT 06/2100Z 13.2N 31.2W 45 KT 50 MPH
12H 07/0600Z 13.3N 33.3W 50 KT 60 MPH
24H 07/1800Z 13.6N 36.2W 55 KT 65 MPH
36H 08/0600Z 13.9N 39.1W 55 KT 65 MPH
48H 08/1800Z 14.3N 42.1W 50 KT 60 MPH
72H 09/1800Z 15.0N 48.5W 45 KT 50 MPH
96H 10/1800Z 16.0N 55.0W 40 KT 45 MPH
120H 11/1800Z 17.0N 61.0W 30 KT 35 MPH

$$
Forecaster Pasch

[OuterBanker]

Pretty good consensus on Grace meeting her demise in the islands. Just like Danny and Erika.

[drewschmaltz]

I understand what the outlook for Grace is but weren't a lot of the models throwing Erika NW above PR then trapped by the ridge and moving WNW whilst undergoing RI? I mean, Erika never stacked vertically and caught the northern route, but weren't the models (mostly) telling a different story? There was never model consensus like this for Erika or am I remembering it wrong?

What I can understand is how Erika's actual path and Grace's models are alike.

[Alyono]

very disorganized based upon the latest WINDSAT pass

[Hammy]

I understand what the outlook for Grace is but weren't a lot of the models throwing Erika NW above PR then trapped by the ridge and moving WNW whilst undergoing RI? I mean, Erika never stacked vertically and caught the northern route, but weren't the models (mostly) telling a different story? There was never model consensus like this for Erika or am I remembering it wrong?

What I can understand is how Erika's actual path and Grace's models are alike.

The problem with Erika is that there was a model consensus for the most part, but they were all basically wrong, though I think the lack of a definitive center could've been to blame, and they may have estimated the storm as being stronger or better handle the environment than it was. In this case I would assume some degree of accuracy compared to Erika, since they have a more organized storm to work with (though I have on idea why the Euro is failing so badly at initialization.)

[Steve H.]

What is that area of convection to the west of Grace? It has been flaring up over the last few days.

[emeraldislenc]

That area drew my attention too it looks pretty good!

[blp]

One thing I am seeing tonight is that Grace has become much smaller with thunderstorms concentrating over a small area close to the center. Reminding me more more of Danny. I think this will also lead to its demise quicker as it hits the shear since it will be more easily disrupted. Lets see what happens.

http://www.ssd.noaa.gov/PS/TROP/floater ... imated.gif

[Weatherlover12]

Even if grace is destroyed by the shear.. Couldn't it come back in the Bahamas because some models have a vort there and I'm sure conditions are favorable right?

[northjaxpro]

What is that area of convection to the west of Grace? It has been flaring up over the last few days.

Actually, that area is a tropical wave which is just past the 40 degrees Longitude point. The wave did flare up a bit of convection during the day, but there is dry air all around that wave which will debilitate this wave from developing. That same dry air may be already impacting Grace now, and with shear forecast to increase late this week, this will kill Grace too unless she can gain latitude approaching the NE Caribbean by the end of this week into the weekend.

[Hammy]

Grace seems to have peaked already, may have been 50kts overnight. Today it seems to be drying out rather than contracting in size, and there's a visible difference in outflow/moisture between the eastern and western periphery, which tells me it may already be running into shear.

[Alyono]

likely already peaked. Wouldn't be surprised if this dissipates in just a couple of days given its small size

[gatorcane]

not looking the greatest lately but even with Danny we remember it also looked like it was going to bite the dust at one point and it came back as a major, albeit compact system. Likely not a major here, but the vorticity is still very strong with Grace looking at the 850MB vorticity charts and let's see if convection makes a comeback later tonight.

[northjaxpro]

likely already peaked. Wouldn't be surprised if this dissipates in just a couple of days given its small size

Yeah, Grace is waning quickly tonight. No deep convection at all around the COC currently. What is interesting is that the tropical wave to the west of Grace is pulsating convection better than she is right now.

[Hammy]

likely already peaked. Wouldn't be surprised if this dissipates in just a couple of days given its small size

Yeah, Grace is waning quickly tonight. No deep convection at all around the COC currently. What is interesting is that the tropical wave to the west of Grace is pulsating convection better than she is right now.

How possible is it that the system west might be sucking enegy from Grace?

[abajan]

... How possible is it that the system west might be sucking enegy from Grace?

Not sure but I think that wave bears watching and certainly has enough convection (for now anyway) to warrant its own thread in our Talking Tropics forum.

[floridasun78]

i notice that i talk about in central Atlantic topic Talking Tropics forum.

[AutoPenalti]

Ooh goody another microcane.