SW Louisiana Forecast Discussion...After a dry start to meteorological autumn, and the month of September big changes are commencing. This is evident today as a better than normal coverage of shower and thunderstorm activity has occurred. This trend will not only continue through the weekend, but rain chances will increase further. The chances for showers and thunderstorms could eventually end up maxing out (100%) this weekend. There are several factors coming together that will dictate how much rain, and the amount of coverage we will see from day to day through Sunday. The forecast is a rather complex one, but I will get into the meat and potatoes of it here shortly. While there will likely be much fine tuning to this forecast in the coming days, the bottom line is we will be in a wet pattern through the weekend, with the rain chances ramping up and peaking over the weekend.
Rain chances were enhanced today by an impulse rotating out of the Rockies, and by an influx of deep tropical moisture from the Western Gulf of Mexico. Rainfall began around late morning as this moisture moved onshore via the sea breeze. Due to the extensive coverage of shower and thunderstorm activity, maximum temperatures were only near normal or slightly below normal. SW Louisiana is on the northern edge of this axis extending along a trough from the Bay of Campeche to the offshore waters south of Cameron. This elongated area of moisture will remain in place for the next couple of days with very little movement. This will keep the forecast area under the influence of very deep tropical moisture directly from the Bay of Campeche in the SW Gulf of Mexico. So, for Thursday rain chances will again be higher than average with them likely to increase further from there. Temperatures will be around seasonable for morning lows, but remain below normal for afternoon highs. An approaching trough and associated cold front coming out of the Rockies will be moving SE as well. The frontal boundary will be in a weakening state as it moves into the offshore waters off the Texas coast tomorrow into Friday. It is at this time, that a surface low may develop along the tail end of this boundary. More on that in a moment.
Regardless of what happens in the Gulf, the influx of tropical moisture will be the dominant weather feature for the Friday through Sunday periods. The area of tropical moisture clustered just offshore will only slowly lift Northward. Rain and thunderstorms will be widespread on Friday especially later in the day, and chances will nearly max out this weekend as the deepest moisture moves inland right over the forecast area. Chances of rain should be about the same for both Saturday and Sunday. Heavy rainfall is a good possibility with several inches of rainfall expected area wide between now and Sunday, and rain chances won't be strictly confined to the afternoon and evening hours. In this type of pattern, a shower or thunderstorm is possible at any time of day or night. Rainfall totals will vary from place to place, but locations that see the heaviest rainfall will run the risk of some localized flooding. Unfortunately, it looks like a good chance of rain for all of the football games this weekend. The timing of when the heaviest rainfall will occur is still uncertain, as models waiver on this idea.
Conditions over the Gulf are only marginally favorable for tropical development, and they should stay this way. Most models do indicate cylcogenesis, but vary on the degree. It is a highly climatological favored time of year for a tropical system to develop as we are at the peak of the season this week. However, a lot of times the models don't understand the amount of shear in a given environment. There is a decent amount of wind shear over the Gulf at this time, but it may relax for a short time late Thursday into Friday, before even stronger shear develops with the presence of the approaching trough. Therefore, I don't believe a tropical system will develop. However, a weak low of subtropical or tropical origins will traverse the Western Gulf, and move into Louisiana over the weekend. Weaker systems often move slower than stronger systems, and therefore, often generate higher rainfall amounts. The weak low will keep the plume of tropical moisture advecting from South to North across the forecast area through the weekend. Hence, the highest rain chances will come over the weekend. Further fine tuning over the next couple of days will determine which day will have higher rain chance. The weak low and associated tropical moisture will be slow to vacate the area, but conditions should improve by Monday.
The other scenario with this very complex weather situation is one that would involve further development of the aforementioned Gulf low. If conditions become more favorable, which, as mentioned earlier, isn't entirely impossible given the time of the year it is, a tropical depression or tropical storm could develop. If this occurs, the area of shower and thunderstorm activity over the Gulf would congeal into a more organized area, and close up into a tighter area. Any possible tropical development in this area will be slow to occur.This would limit shower and thunderstorm chances over the forecast area at least initially as subsidence over land increases with an organized cyclone in the SW Gulf of Mexico. The onset of the heavy rains would likely still be over the weekend, but conditions would be much drier across the area on Friday. However, an organized system such as a tropical depression or tropical storm would make conditions worse over the weekend as some wind is thrown into the equation, and a coastal flooding threat would exist as well. This is NOT forecast to happen at this point, and this situation is to be re-defined as necessary in the coming days.
As for the remainder of the forecast period...Conditions improve on Monday as the Gulf low advances NE into Mississippi ahead of the advancing trough and stalling front. Some drier air will filter into the region on the backside of the low as winds shift from offshore to onshore. With the frontal boundary in the region, shower and thunderstorm activity will still be in the forecast as this will be a focusing mechanism during daytime hours for the development of showers and thunderstorms. Monday will still offer above normal rain chances especially in the Eastern portions of the forecast area in closer proximity to the departing low, but essentially a normal mid-September pattern is forecast at this time. A secondary and stronger cold front will be moving into range towards the end of the forecast period. The timing of when this front makes it through is still uncertain right now as models flip flop on the issue, but it appears to be just beyond the scope of this forecast period. If the front speeds up, then rain chances will go higher in latter portions of the forecast period. Temperatures during the Monday-Wednesday period will be near seasonal. Of note, mid-September is the climatological peak of hurricane season, but it is also the time when we typically see our first cold front of the season. Stay tuned for further fine tuning to this forecast in the coming days.
Tropics: Hurricane Fred is the only active system. It has weakened some from major hurricane status in the far Eastern Atlantic, and this is where it will stay. Fred is being steered to the North by a weakness in the Atlantic ridge off the coast of Africa. This will keep Fred on a course to remain over the open waters of the Far Eastern Atlantic, and he will not be a threat to anyone except ships in that region. Fred will move into colder waters in the coming days, and weaken into a tropical depression if not a remnant low within 5 days. Fred is the second hurricane and second major hurricane of the 2009 season. Fred will be pretty to look at on satellite, but that's about the only interest it will have to us. I will continue to update the forecast track of Fred, but this is really about the only time I will discuss him in detail. The weakening trend with Fred has already begun tonight with Fred feeling the influence of increasing shear and dry air entrainment on the West side of the storm. Weakening is forecast for the entire forecast period as shear is forecast to increase and as the system moves into colder waters.
Here's the latest advisory on Hurricane Fred from the National Hurricane Center:
Hurricane Fred 10p.m. Wednesday, September 9, 2009
Latitude: 15.3N
Longitude: 33.7W
This is about 645 miles West of the Cape Verde Islands.
Wind: 105 mph w/ higher gusts- Category 2. A continued weakening trend is forecast for the next few days. Hurricane force winds extend outward to 30 miles from the center while tropical storm force winds outwards to 115 miles from the center.
Motion: NW at 10 mph---this motion will continue tonight, but a turn to the NNW and a decrease in forward speed is expected on Thursday. This will be followed by a turn to the North and NNE on Friday.
Pressure: 28.50" or 965 mb.
Elsewhere in the tropics, no tropical storm formation is expected through Thursday.
Preliminary Numbers & Zone Forecasts:
LCH 73/86 73/84 75/83 20 60 30 70 40 80
LFT 72/87 73/85 74/84 20 60 30 70 40 80
BPT 74/85 75/84 75/83 20 70 30 80 40 70
AEX 70/88 71/86 74/85 10 50 20 60 30 70
POE 71/88 72/86 74/85 10 50 20 60 30 70
ARA 74/87 75/84 76/84 20 60 30 70 40 80
Tonight...Partly to Mostly Cloudy with a 20% chance of showers and thunderstorms after midnight. Low 73. SE wind 5-10 mph.
Thursday...Mostly Cloudy with showers and thunderstorms likely. High 86. SE wind 10-15 mph. Chance of rain 60%.
Thursday Night...Mostly Cloudy with a 30% chance of showers and thunderstorms. Low 73. SE wind 5-10 mph.
Friday...Cloudy with showers and thunderstorms likely. Locally heavy rainfall possible. High 84. SE wind 10-15 mph. Chance of rain 70%.
Friday Night...Mostly Cloudy with a 40% showers and thunderstorms. Low 75. SE wind 10 mph.
Saturday...Cloudy with showers and thunderstorms likely. Locally heavy rainfall possible. High 83. SE wind 15-20 mph and gusty. Chance of rain 80%.
7 Day Outlook for Lake Charles & Vicinity
Thursday
9-10-09
73/86/60
Wind: SE 10-15
H.I.: 90-95
U.V.: 8- High
Friday
9-11-09
8 Year Anniversary of 9/11 Terror Attacks
73/84/70
Wind: SE 10-15
H.I.: 90-95
U.V.: 8- High
Saturday
9-12-09
75/83/80
Wind: SE 15-20
H.I.: 90-95
U.V.: 7- Medium
Sunday
9-13-09
1 Year Anniversary of Hurricane Ike & 2 Year Anniversary of Hurricane Humberto
76/84/80
Wind: SE 10-20
H.I.: 90-95
U.V.: 7- Medium
Monday
9-14-09
75/88/40
Wind: SE 10-15
H.I.: 90-95
U.V.: 9- High
Tuesday
9-15-09
71/90/30
Wind: SE 10-15
H.I.: 95-100
U.V.: 10- High
Wednesday
9-16-09
72/90/30
Wind: South 10-15
H.I.: 93-98
U.V.: 11- Very High
...Marine Forecast from NWS Lake Charles...
Tonight...Southeast winds 5-10 knots becoming east after midnight. Seas 1-2 feet.
A chance of showers and thunderstorms.
Thursday...Northeast winds around 5 knots becoming east in the afternoon. Seas 1-2 feet.
Showers & Thunderstorms Likely.
Thursday Night...East winds 10-15 knots. Seas 1-2 feet.
Numerous showers and thunderstorms.
Friday...ESE 15-20 knots. Seas 1-3 feet. Numerous showers and thunderstorms.
Friday Night...Southeast winds 10-15 knots. Seas 2-3 feet.
Numerous showers and thunderstorms.
Saturday...South winds 10-15 knots. Seas 2-4 feet. Showers and thunderstorms likely.
Thursday Tides:
Low: 1:03 a.m. 2:20p.m.
High: 4:01a.m.
Climate Data from NWS Lake Charles...
Wednesday, September 9, 2009
Low: 73
Normal Low: 71
Record Low: 59-1918
High: 86
Normal High: 89
Record High: 98-1906
Precipitation:
Rain Today: 1.07"
Month to Date: 1.08"
Normal Month to Date: 1.81"
Year to Date: 42.80"
Normal Year to Date: 39.90"
Sunrise Thursday: 6:55a.m.
Sunset Thursday: 7:24p.m.
Good night and God Bless!
-DM-
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