Talking the Tropics With Mike: Ante is “upped” for Gulf Coast: Marco & Laura are twin threats

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LOCAL - JAX/NE FL./SE GA. impacts from current tropical activity: ** None of consequence ** ... but folks anywhere along the Gulf Coast from Florida’s Panhandle to Texas - need to stay up to date on future forecasts regarding the tropics as fast changes/development will be possible into next week.

Any local impacts from tropical storm Laura look to be relegated to a slight bump in waves & surf through early next week & a bit of a surge of tropical moisture from the east increasing rain slightly. No significant direct local impacts are anticipated while current tropical cyclones take the “low road” - Marco far to the west & Laura well to the south then well to the west.

According to Phil Klotzbach, “hurricane guru” @ CSU, this will be only the 3rd time since 1851 that there have been simultaneous Gulf of Mexico storms with winds 39+ mph (tropical storm strength): Sept. 5, 1933 & June 18, 1959 (especially impressive - early season!).

LAURA:

Strong tropical wave ’98-L’ was upgraded to tropical depression #13 Wed. then to tropical storm “Laura” Fri. while steadily moving west & approaching the NE Caribbean. This is the fastest to the 12th storm breaking the record of “Luis” on Aug. 29, 1995. As the Bermuda High to the north expands & strengthens, Laura should continue a steady track west before a slow bend to the northwest & forecast models are in excellent agreement on such. This pushes the system from near Puerto Rico Sat. ... near or over Hispaniola by early Sunday... & near or over Cuba late Sunday into Monday. There remains a reasonable chance - as has been the case in recent days - for a track farther south as the Bermuda High flexes its muscles. There is also an argument for a more southern route (more westward movement) if the tropical cyclone remains weak. Land interaction looks to be more of a factor leading to likely disruptions in its organization resulting in complications with the overall forecast - both track & especially intensity. Satellite & radar data seem to show an organizing tropical system through Saturday with an increase in the upper level outflow. The center may very well jump around some until the cyclone is more organized. If the center somehow manages to reform away from the Greater Antilles with less time over land, Laura could end up strengthening faster than currently indicated followed by at least a somewhat earlier turn to the north.

Intensity continues to be a difficult forecast which is not unusual but even more so in the case of Laura. Several of the typically more reliable models - the European & GFS, for example - have been showing little strengthening... & even weakening in some forecast cycles but are then stronger in other cycles. The UKMET - notoriously too strong this season so far - had been trending weaker & more south & west but has recently strengthened again though seems to be having some problems resolving the two tropical cyclones vs. one. I’m still concerned about a “late bloomer” on this one. A tropical cyclone that’s relatively weak possibly until making it into or near the Gulf of Mexico by Monday. Once in the Gulf (or far Northern Caribbean) & away from any land areas, there should be a gradual turn more northward. There will be heavy squalls this weekend for parts of the Northern Lesser Antilles as well as Puerto Rico, Hispaniola & eventually Cuba though impacts do not look to be severe, there will be a distinct threat for flash flooding & landslides. In addition to land interaction, there is some dry air in the path of Laura which could serve to limit intensification, especially in the shorter term but shear has been weakening. The low & mid level centers of Laura have not been in sync for some time now with multiple swirls & small scale low pressure areas evident on satellite & radar data but a more defined/stacked system appears to be evolving. Until & unless the centers become aligned, strengthening will be limited. In any case, the trend is for a tropical cyclone more to the west across the Gulf of Mexico taking Florida “out of play” but increasing the ante for the Gulf Coast from Texas to Alabama.

MARCO (Major shift east in the ultimate landfall!):

Tropical wave ’97-L’ has continued west after entering the Caribbean Mon. night & has been upgraded - as of Thu. morning - to tropical depression #14 & then to tropical storm “Marco” Fri. evening. Marco has been slowing some & turning more northward as it gets to the western edge of the now sprawling Bermuda High over the Atlantic & this is where we’ll have to pay close attention. In fact, Marco missed most of the potential land interaction with the Yucatan Peninsula which has upped the ‘ante’ for strength & subsequent impacts along the Gulf Coast including New Orleans. While looking rather “healthy” Thu., the depression became pretty disheveled Thu. night only to see bursts of convection Fri./Fri. evening & seems to be gaining organization since late Fri. At least a tropical storm & possibly a hurricane will threaten the Central & Western Gulf of Mexico by the early to middle part of next week. There will be a fairly strong & large area of shear developing over the Western Gulf which may serve to limit overall strengthening of Marco in the longer term upon approach to land, but it’s possible that this hostile environment will be a little late &/or a little west before having significant impacts on the storm.

Meanwhile.... complicating things even further... an upper level trough of low pressure has built southward over the Gulf coast states & Gulf of Mexico & will be lifting northward over the next couple days. Once this feature leaves the area, it appears there will be some room for the Bermuda High - or an extension of the upper high - to build into the area. How exactly this plays out will probably have at least some role in how Marco & Laura are steered - & where they eventually go. It’s this “weakness” in the flow that has likely allowed Marco to turn more northward earlier. Forecast models continue to bounce around but it’s worth noting that conditions may become favorable enough for significant strengthening of either or both Marco & Laura.

There has been quite a bit of scuttlebutt regarding a possible “Fujiwhara effect” between Marco & Laura. Right now I see the two systems as remaining their own separate entities, so I’m not going there. Eventually there could be some outflow interaction next week depending on where the systems are & how strong they are (tropical cyclone Fujiwhara effects have happened in the past, by the way). But no need for a lot of hype(!) on this possibility.

Overall conditions across the Atlantic Basin appear “ready to go” as we head into late Aug. & early Sept. (see velocity potential anomalies map below). I’m tracking a long track tropical disturbance soon to move westward across the Atlantic that could threaten some part of the U.S. between ~Sept. 1 & Sept. 9th.

Lots of spaghetti(!):

Lots of rain along & near the Gulf Coast into next week due to a combination of tropical activity & an upper level trough with extreme rainfall possible from the upper Texas coast to the far Western Fl. Panhandle:

A change of phase of the MJO (Madden-Julian oscillation) should help lead to an uptick in Atlantic tropical cyclones late this month into September. The upper level “velocity potential anomalies” map below shows “upward motion” - green lines - spreading east from the already active E. Pacific. Such a pattern often correlates to an increase in tropical systems that would eventually include the Atlantic Basin.

A strong tropical wave over the Eastern Atlantic is marching west. Forecast models are not jumping on this one yet but something to keep an eye on....