Caribbean Disturbance to bring Rain to the GOM, and may Develop

By: Levi32 , 2:52 PM GMT on June 19, 2012

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We are continuing to monitor the Gulf of Mexico for tropical development later this week, through the weekend, and into early next week. We now know the instigating disturbance is a tropical wave coming northwestward out of the Caribbean into the central-eastern gulf while interacting with the monsoon trough over central America. Right now a broad, elongated area of showers and thunderstorms is covering the Caymans, Cuba, and the Bahamas. This activity will be spreading northward over the next couple of days, encompassing all of the Bahamas and Florida, bringing heavy rains of many inches to some places. At this moment, only a weak mid-level turning is noted the western Caribbean, with most of the associated convection sheared off to the east, and overall the area is a complete mess right now. However, an upper low over the central Gulf of Mexico will be moving northward out of the way during the next 72 hours, allowing another upper low over northern Mexico to ventilate the gulf and allow an upper ridge to expand northward, lowering wind shear and providing a more favorable environment for consolidation of a tropical low. Due to the elongated nature of the pattern we are dealing with, the setup will likely not be optimal, but should be favorable enough to allow gradual development.

The models are still heavily diverging on the fate of this system immediately after 48 hours out, which is an impressive disagreement for the time period being so close to us now. The GFS for a couple of days now has started taking most of the moisture out to the northeast over Florida and into a trough over the eastern seaboard, while letting the low in the Gulf of Mexico die at 90W. I attribute most of this forecast behavior to a typical GFS bias where the model tends to throw the energy away poleward into a trough that it deepens too much into the tropics, an error that it makes a lot during strong MJO pulses. The GFS's MJO forecast is also unrealistically strong in phase 1, which is likely causing feedback problems in our area of the world, which immediately calls into question its forecast in the tropics for the next several days. The CMC had previously taken the low northward towards the Carolinas as well, but such forecasts I am dismissing as unrealistic at this point. Most of this activity should eventually shift westward into the NW Gulf of Mexico with time, under a pattern very similar to Allison in late June 1989 as we have been discussing recently. The NAEFS and CMC ensemble means continue to support this idea.

Should this system develop, it will take its time in organizing, and likely won't get terribly strong, unless it gets more time over water than expected, but a tropical storm is very possible in this pattern, and environmental conditions will be improving with time over the gulf. Development or not, a shot of rain is likely to get into the NW gulf and affect at least south Texas and northern Mexico. Rain will be harder pressed to get as far north as Houston and Louisiana, but that will depend on the exact track of the system once it gets into the gulf. Interestingly, many forecasts along the NW gulf coast are calling for sunny conditions for the next week, and it will be interesting to see if they get surprised. Overall, the general idea that we have been working on for the last couple of weeks has not changed, and a development threat in the western-central Gulf of Mexico will be spreading rain around from east to west as we move through the end of this week and into early next week.

We shall see what happens!

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12. biloxibob
11:23 PM GMT on June 20, 2012
Thanks Levi. An excellent synopsis. I didn' know you were a physics major.My minor was physics.ended up going to medical school in the 70s.
Member Since: August 21, 2011 Posts: 0 Comments: 138
11. Hoff511
8:42 PM GMT on June 19, 2012
Thanks Levi!
Member Since: September 2, 2009 Posts: 0 Comments: 265
10. aislinnpaps
6:28 PM GMT on June 19, 2012
Thank you, Levi
Member Since: August 22, 2009 Posts: 0 Comments: 3167
9. LakeWorthFinn
5:01 PM GMT on June 19, 2012
Thanks Levi, I learn a lot from you :)
Member Since: October 6, 2005 Posts: 68 Comments: 7515
8. AtHomeInTX
5:01 PM GMT on June 19, 2012
Thanks Levi. I hope south TX does get its rain without the winds. :)
Member Since: August 24, 2010 Posts: 0 Comments: 258
7. Patrap
4:53 PM GMT on June 19, 2012
The Local NWS folks along the GOM are not surprised, its mentioned in all the Disco's.

Area forecast discussion
National Weather Service New Orleans la
834 am CDT Tuesday Jun 19 2012


overall...a fairly quiet weather regime is still expected to be
in place for the forecast area through the week with the main
forecast issue being temperatures...that is increasing daytime
high temperatures. Ridging at the surface and aloft will dominate
the Gulf Coast region during at the least the majority of the
period. Precipitable water values derived from satellite data
indicate drier air entrenched across the eastern two thirds of the
forecast area. As a result...will only include a slight chance for
showers and thunderstorms over the western most sections of the
forecast area today. As the dry Continental airmass continues to
make its way westward with the upper ridge building over the
region...Wednesday and Thursday look to be dry. The GFS and European model (ecmwf)
continue to disagree in the medium range with regard to a trough
in the Caribbean that is forecast to move across the Gulf during
the later part of the week and through the weekend. The GFS
solution is farther north and forecasts less in the way of ridging
aloft over the central Gulf Coast region than that of the European model (ecmwf)
during that period. In addition...the GFS develops a surface low
over the central or north central Gulf while the European model (ecmwf) moves a
surface low westward on a more southern Route. Although both the
GFS and European model (ecmwf) keep the bulk of the moisture associated with this
feature south of the area...a more northerly solution as indicated
by the GFS could lead to a slightly better chance for convection
for the Friday through Sunday time well as hold down
temperatures a bit. At this time...we plan to keep a mostly dry
forecast with a slight chance for convection mainly across the
coastal waters and adjacent coastal areas late in the week and
over the weekend. High temperatures are expected to be a little
above average...mainly into the lower to middle 90s.
Member Since: July 3, 2005 Posts: 431 Comments: 131377
6. HurricaneOwen99
4:40 PM GMT on June 19, 2012
Nice and detailed update, thank you!
Member Since: June 18, 2012 Posts: 0 Comments: 12
5. nigel20
4:16 PM GMT on June 19, 2012
Thanks for the update!
Member Since: November 6, 2010 Posts: 14 Comments: 8766
4. BobCarver
4:14 PM GMT on June 19, 2012
Thanks for the update, Levi. GEOS-5 looks promising. Where do you get your updates from that model?
Member Since: May 18, 2010 Posts: 0 Comments: 3
3. HurricaneDean07
4:06 PM GMT on June 19, 2012
Thanks Levi
Member Since: October 3, 2010 Posts: 40 Comments: 4129
2. TropicalAnalystwx13
3:22 PM GMT on June 19, 2012
Thanks Levi.

I don't care if it's a weak, moderate, or strong tropical storm, as long as it is not ugly and sheared to death. Hate those.
Member Since: July 6, 2010 Posts: 113 Comments: 33630
1. kwgirl
3:21 PM GMT on June 19, 2012
Thanks Levi. It is raining right now in Key West so I am happy for my plants and a little sad I might have to miss my water aerobics. We need the rain though. Last week when the mainland was getting pounded, we got nothing.
Member Since: March 28, 2008 Posts: 0 Comments: 1532

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Masters student in tropical meteorology at FSU. Raised in Alaskan blizzards, but drawn toward tropical cyclones by their superior PGF.

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