Thursday, June 06, 2013

Andrea Pushes Towards Florida, Heavy Rains To Push North

The season's first tropical storm is pushing northward through the Gulf of Mexico towards landfall along the Florida Panhandle later tonight.  Andrea's calling card, like most early season tropical entities, will be lots of rainfall as it pushes north.  It is slightly better organized this morning compared to yesterday but still has a fair bit of wind shear to do with in the Gulf of Mexico as well as dry air.  This water vapor image shows the amount of dry air (in red and orange hue) to the west of the comma shape swirl that is Andrea's circulation.

Due to the presence of that dry air and wind shear, the strongest winds and the vast, vast majority of precipitation with Andrea is on the eastern side of the storm at present.  This storm will pull that moisture north and then northeast up the coast.

Andrea's north and northeast trek is influenced by a trough that's digging across the Ohio Valley (to the north of the storm).  These two features (don't worry about those storms in OK and TX) will tag team through our region and produce a pretty heavy rain event for us tomorrow and tomorrow night.  Rains will move into the western parts of the region late today -- influenced by the trough's approach, not by Andrea -- with Andrea's influence on our pattern in line for tomorrow through tomorrow night.

Modeling still have a fair bit of variance on where the heaviest rains will fall.  The GFS is suggesting the heaviest rains will fall right at the coast or just offshore, with the Euro suggesting that the heaviest rains will be along I-95. The NAM, outside of one run early this morning, has more often than not shown the heaviest rainfall axis to be aligned to the city's west.  The max on rain is generally in the two to three inch range on the average although isolated three inch plus amounts aren't out of the realm of possibility.  If the GFS scenario pans out, most of us are closer to an inch than three inches.

Since this system will be interacting with an approaching frontal boundary and trough, the left of track rainfall axis that often accompanies tropical systems that are becoming nontropical entities probably applies here.  That would suggest the Euro or NAM may ultimately be right for heaviest rains.  The GFS' axis of heavier rainfall is just right of the low track.

The rainfall piece is the single biggest player in our discussion for this system -- wind will not be a huge issue locally although it may be a bit breezy at the Shore tomorrow afternoon and evening.  Areas that are prone to flood pretty easily may do so in this storm tomorrow evening with the bulk of the heaviest rains.

Rains will begin to move in tonight -- although those are NOT directly associated with Andrea. The front's approach will spread showers in, some of which could be locally drenching overnight.  Rains will pick up in intensity tomorrow from midday on, with the PM rush into the evening hours the most likely time for heavier rainfall.