General Discussion >> 2023 Forecast Lounge

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Harold Lounge
      #114617 - Wed Aug 16 2023 02:03 PM

A seemingly slow start to the Atlantic Hurricane Season in and around the Gulf of Mexico, but models are now homing in on development very close to home within the next seven days.

The view from 50,000'
A moisture surge is set to approach and cross Florida over the weekend and multiple models spin this feature up. Additionally, a CAG (Central American Gyre) or something at least close enough to meeting a more formal definition, is likely to develop over the next several days, and help promote the production of one or more tropical cyclones in the western Atlantic. These will also benefit from the development of a belt of low-level westerly anomalies creating cyclonic background vorticity across the tropical Atlantic, very uncharacteristic of El Niños. The ECMWF ensemble has also shown an overlap of anticyclonic wave breaking over this forecast enhanced vorticity in the western Atlantic and Gulf of Mexico, which can further encourage "home grown" genesis.

ECMWF currently suggests around a 40-50% chance of development close to Florida over this weekend into early next week, increasing to 65% by the time the forecast area of interest is in the central to western Gulf by the middle of next week (Aug 23-24 or so). The GFS also develops this region.

While a disturbance for an Invest tag to be assigned has yet to appear, this now looks probable, and as such we are starting this lounge. An Invest number will be assigned and added to the title should these forecasts verify.

We are now in the climo peak of the Atlantic basin, and climatology shows us that systems in this part of the basin around this time of year can go from zero to a real threat quickly. NHC opening odds of development are set at 20%, and this could be conservative.

The forecast Gulf disturbance has become defined enough to be assigned an Invest tag, 91L, and the title has been updated accordingly.
PTC-NINE on 8/21/10CT -Ciel

Edited by cieldumort (Tue Aug 22 2023 02:04 AM)

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Re: 91L Lounge [Re: cieldumort]
      #114628 - Sun Aug 20 2023 06:58 PM

Above: Invest 91L Aug 20 5:16pm CT

91L is becoming a more coherent area of low pressure today now that it is indeed in the eastern Gulf of Mexico. Conditions for further development are favorable, and it is more likely than not to earn a name this week. 91L is primarily an open water and then Texas/Mexico threat.

Here are some recent model rundowns

20/18z Experimental RRFS-A (National Oceanic and Atmospheric Administration’s next generation convection-allowing, rapidly-updated ensemble prediction system, currently scheduled for operational implementation in 2024). This model seems to have a close handle on the initial state of 91L as of this evening, and also does a much better job than most at incorporating convection and its impacts "convection allowing.": Very stout tropical wave until 91L is in the central GOM Monday afternoon, where this model's run seems to have the system unmistakably closed off as a strong tropical storm. Cat 1 hurricane Tuesday morning on approach to south Texas. Landfall later Tuesday morning as a strong Cat 1 in the vicinity of Port Mansfield, TX.

20/18z NAM3K (Also convection-allowing, but does not appear to have as good a handle on initial state): Landfall in extreme South Texas near Brownsville Tuesday morning as a T.D. or low-end T.S.

20/18z GFS: (A less organized initial state than the RRFS. Not convection-allowing): Landfall Tuesday morning in vicinity of Port Mansfield, TX as a low-end T.S.

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