Katia rapidly intensifies, Lee makes landfall

Not much changed since my last update on Friday... Katia has been hovering on the 60-65kt mark, which also means switching between TS and hurricane each time (fairly big name shift for a very minor change in wind speed).  The vertical shear has been much slower to let up than forecast (except for the GFDL model, which did see this extended period of high shear, but it was an outlier), and as a result, Katia did not intensify as forecast... but also didn't weaken much either.  However, conditions have improved over the past few hours, and the storm was quick to respond in a big way.  The intensisty as of 15Z today has skyrocketed up to 85kts with a central pressure of 966mb, and a open, clear eye is forming... it was a 60kt TS with a pressure of 992mb six hours ago!  The center is about 375 miles northeast of the northern Leeward Islands.  The forecast is still for additional intensification, and for a continued northwest track; it's looking quite likely now that Katia will recurve prior to reaching the US east coast, AND stay to the west of Bermuda.

Shortly after my update on Friday, TD13 was upgraded to TS Lee based on aircraft recon.  Since then, it did not intensify much, but as expected, remained a large amorphous rainmaker, crawling along at 2-5kts.  It made landfall about 50 miles west of Morgan City with 40kt sustained winds.  But more importantly, the rain keeps falling. 

There has already been up to a foot of rain across the southern coast, from LA to AL, over the last 3 days.  More will come today and tomorrow. Lee should still be over southern LA for at least another day, then begin accelerating to the northeast ahead of a mid-latitude trough... tracking over MS, AL, and TN over the next 3-4 days.  The graphic below shows the estimated rainfall totals over the past 4 days in the region:

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Katia hanging on, TD13 forms in Gulf

Katia actually went against model guidance again and weakened a bit to a strong tropical storm yesterday afternoon, but has since reintensified to a minimal hurricane (65kts, 991mb).  The vertical shear was quite a bit stronger than forecast, and it definitely took a toll on the storm.  However, with shear dropping from 20kts to 10kts over the next couple of days, Katia should be able to resume the previous strengthening trend.

The official forecast calls for gradual intensification to 100kts (Cat 3) over the next 5 days as it heads WNW... with a 5-day (Wednesday) position located about 500 miles north of Puerto Rico.  The long-term future is still too uncertain as to whether it will recurve before reaching the US east coast or not, but extended-range models generally indicate a safe recurvature.  Certainly something to keep a very close eye on anywhere along the east coast though.

The disturbance that I first mentioned on Tuesday has been upgraded to TD13, and is not far from becoming Tropical Storm Lee.  This disturbance was way back by the Lesser Antilles on Aug 25, so it's been "on the radar" for a week now.  It is organizing very quickly now that the vertical shear is relaxing -- from 25kts to 5kts over the next 24 hours.  The intensity is 30kts, it's centered just 190 miles southwest of New Orleans, it's nearly stationary, and the outer rainbands are already onshore.

Tropical Storm warnings are up for the entire LA and MS coast... the latest forecast track, watches, and warnings can always be found at http://www.nhc.noaa.gov/storm_graphics/AT13/refresh/AL1311W5+gif/145613W_sm.gif

The 5-day accumulated precipitation forecast from HPC is still very ominous for the southeast, with 1-2 feet of rain possible over southern LA and MS.  You can watch the regional radar loop showing the extent of the rainfall at http://radar.weather.gov/Conus/southmissvly_loop.php 

This flooding rain will be combined with perhaps multiple days of tropical storm force winds, and I wouldn't be surprised at all if some evacuations were ordered for New Orleans, Biloxi, Mobile, Pensacola, and other urban flood-prone cities in the area (as well as offshore oil rigs).  If you or someone you know is down there, keep a close eye and ear to the local tv and radio stations this weekend.

Finally, the circulation that was north of Bermuda yesterday has not moved much at all, but is actually even more sheared than it was... making any development unlikely.  What convection there is in association with this system is displaced far to the northeast, and while the SSTs are fairly high now (28C), they will plummet to 22C within a day as it moves to the northeast.

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Katia now a hurricane, Gulf disturbance organizing

Welcome to September, by far the busiest month of the Atlantic hurricane season!

As of this morning, Katia was upgraded to a hurricane (second of the season) with 65kt sustained winds and a 987mb central pressure. 

It's located about 850 miles east of the Lesser Antilles and heading W at 16kts.  This westward motion was not anticipated... models have been in excellent agreement that the WNW or even NW track would persist.  This could suggest that the more southern models among the guidance package could be on the right track.  The models also collectively suggest a continued gradual intensification (shear is an inhibiting factor, but not strong enough to be too detrimental).

The disturbance that was near the northern Yucatan peninsula yesterday is now well into the Gulf (AL93).  It has persistent deep convection, but is in about 20kts of vertical shear.  This is forecast to let up over the next couple of days, perhaps allowing this to organize.  The next name on the list is Lee.

The current NW heading should also come to a halt as it encounters a region with little or no steering flow, leaving it to drift very slowly just off the northern Gulf coast... possibly bringing a major flooding threat with it.  The graphic below from NOAA/HPC shows the forecast 5-day rainfall totals.  Yes, that's an 18.9" bullseye over southern LA.  Whether this storm becomes a TS or hurricane seems like a minor point compared to the flooding potential.

There is also a small and highly-sheared circulation north of Bermuda that bears watching (AL94).

Please visit my tropical Atlantic headquarters.