SW Louisiana Forecast Discussion...The area was indeed dry slotted on Friday on the subsident side of Tropical Storm (now Depression) Bonnie. Granted, Bonnie isn't very strong, and it isnt' a classic looking tropical system by any means, but the subsident zone is always on the Western side of cyclones no matter the intensity, so it is what it is. With the lack of rainfall across the area, temperatures reached above normal levels into the mid 90s after morning lows in the mid 70s. All is quiet tonight as well, but some mid and high level cloudiness out ahead of Bonnie is beginning to move into SW Louisiana, and this will be a sign of things to come as we head into Saturday. Partly to Mostly Cloudy skies should prevail overnight with low temperatures generally in the mid 70s again. A very light offshore flow will occur as well.
The entire forecast at least through Tuesday hinges on Bonnie's eventual track and movement. Certainly, the weekend will be starting on a dry note as the zone of subsidence remains over SW Louisiana for at least part of the day. As Bonnie begins to approach the coastline by Saturday night, clouds will continue to increase, and as moisture content increases, the chances for rain from the outer rain bands will increase as well. The cyclonic flow around the storm will keep our winds blowing from an offshore direction (NE) through Saturday. Most of the daylight hours should be dry across most of the forecast area, but Eastern sections to the East of Lafayette could see some squally weather in the afternoon as Bonnie approaches. Rain chances will be back in the forecast with generally about 30-40% of the area experiencing some tropical rains on Saturday. The rainfall will also be enhanced by the usual effects of daytime heating, but with the offshore flow the presence of a sea breeze will be absent. High temperatures should reach the low to mid 90s once again before things cool off by Sunday. Rain chances continue to increase some on Saturday night as Bonnie nears landfall likely over SE Louisiana, maybe as far West as the Atchafalaya Basin around Morgan City. The outer rain bands will rotate across the forecast area from time to time. On the west side of the system, rainfall should not be widespread or persistent. It will just kind of come and go, and since this is a small storm that will likely be the nature of the game. More moist air associated with Bonnie and the increased moisture will keep low temperatures in the upper 70s for most.
The Sunday-Tuesday period will continue to depend on Bonnie. Rain chances will shoot up into the likely category on Sunday as copious amounts from Bonnie arrive, and remain in place over the area even after the circulation from Bonnie begins to spin down and decay. Rain will be more likely, and more widespread the further East you go on Sunday. Heavy rainfall will be the main threat across the forecast area. Wind will have very little in the way of an impact across the area. A flood threat should not be a great concern, because we aren't expecting more than 1-3" of rain. We are still in drought conditions, and we will be on the dry side of the storm initially, and this will reduce rainfall amounts over the area. Locations along and to the right of the center, will likely see rainfall in excess of 5" through Tuesday. Rainfall chances will remain high through Tuesday because of the orientation of the remnant surface low. It should be over North Louisiana by Monday, and with a low in this location that will open up the Gulf and help establish a long fetch onshore flow across the region. This will keep deep tropical moisture flowing across the area, therefore high rain chances are in the fold through Tuesday. As it stands right now, I have pegged Monday as the day with the highest chance for rain across the area as this will be the day when Bonnie makes her closest approach to SW Louisiana. The temperature regime for the Sunday-Tuesday time frame will also reflect the increased rain chances. Morning lows will be in the upper 70s to around 80 with plentiful tropical moisture in place preventing us from reaching maximum radiational cooling potential. Afternoon highs will hover right around the 90 degree threshold Sunday-Tuesday. The entire forecast for this period is subject to large errors in this situation due to the eventual track of Bonnie. There is still some possibility that Bonnie will move further West closer to SW Louisiana, since it will be a weaker storm. Whether Bonnie comes ashore as a weak tropical storm, tropical depression, or just an open wave weather conditions won't really be all that different across SW Louisiana.
A transition back to a normal summer pattern should take shape by the time we get to the mid-week period on Wednesday. The lingering moisture from Bonnie will only slowly scour out. As Bonnie's remnant moisture begins to vacate the region, we will be situated on the Western edge of the same anticyclone that is helping to steer Bonnie at present. This will favor a sea breeze type set up with the effects of daytime heating leading to shower and thunderstorm genesis during the afternoon. An average chance for scattered showers and thunderstorms for late July is expected on Wednesday. Temperatures should generally be about average for Wednesday as well with low to mid 90s in the offing. Heat indices could reach into the danger category thanks to higher dew points from the remnant moisture of Bonnie. Thursday and Friday offer up a drying trend as the models suggest another visit from the upper ridge. This will create a reduction in rain chances for the Thursday-Friday time frame. Only a 20% of showers and thunderstorms is displayed at this time for the end of the forecast period. Of course, you have heard this many times already this summer...this means that temperatures will also heat up once again with highs returning to the mid to upper 90s with heat indices flirting with the dangerous category of 105 once again. Again, this entire forecast hinges on what the fickle Ms. Bonnie does. The long range forecast suggests a very hot end to the month of July next weekend compliments of a strengthening upper level ridge. Limited shower and thunderstorm activity is expected at this time as well.
Preliminary Numbers & Zone Forecast:
LCH 77/94 78/90 79/89 0 30 40 60 50 70
LFT 79/93 79/89 78/90 0 40 50 70 60 70
BPT 78/95 79/92 78/91 0 20 30 60 40 60
AEX 75/95 75/91 76/90 0 30 50 70 50 70
POE 75/95 75/91 76/90 0 30 40 60 60 70
ARA 78/92 80/89 80/90 0 40 60 80 70 70
Today...Partly to Mostly Cloudy with a 30% chance of showers & thunderstorms this afternoon. High 94. NNE wind 10-15 mph.
Tonight...Mostly Cloudy with a 40% chance of tropical showers. Some heavy rain possible. Low 78. NE wind 15-20 mph.
Sunday...Mostly Cloudy & Breezy with occasional tropical squalls. High 90. ESE wind 15-25 mph and gusty. Chance of rain 60%.
Sunday Night...Mostly Cloudy with off & on tropical squalls. Low 79. SSE wind 15-20 mph. Chance of rain 50%.
Monday...Mostly Cloudy with showers & a few thunderstorms likely. Heavy rainfall possible. High 89. SSE wind 10-15 mph. Chance of rain 70%.
Drew's 7 Day Outlook
Saturday
7-24-10
Low: 77
High: 94
Rain: 30%
Wind: NNE 10-15
H.I.: 98-103
U.V.: 11- Very High
Sunday
7-25-10
Low: 78
High: 90
Rain: 60%
Wind: ESE 15-25
H.I.: 100-105
U.V.: 8- High
Monday
7-26-10
Low: 79
High: 89
Rain: 70%
Wind: SSE 10-15
H.I.: 98-103
U.V.: 8- High
Tuesday
7-27-10
Low: 78
High: 91
Rain: 60%
Wind: SSE 10-15
H.I.: 98-103
U.V.: 9- High
Wednesday
7-28-10
Low: 77
High: 93
Rain: 30%
Wind: SSE 10-15
H.I.: 102-107
U.V.: 10- High
Thursday
7-29-10
Low: 75
High: 95
Rain: 20%
Wind: S 10-15
H.I.: 105-110
U.V.: 11- Very High
Friday
7-30-10
Low: 76
High: 97
Rain: 20%
Wind: SSW 10-15
H.I.: 105-110
U.V.: 11- Very High
...Tropical Outlook...
See the previous post for all the latest on the very disorganized Tropical Depression Bonnie. Landfall is about 24 hours away, and it should occur somewhere in SE Louisiana.
...Marine Forecast...
Saturday...East winds 5 to 10 knots. Seas 1 to 3 feet. A slight chance of showers and thunderstorms.
Saturday Night...North winds 5 to 10 knots becoming northwest after midnight. Seas 2 feet. A chance of showers and isolated thunderstorms.
Sunday...West winds 5 to 10 knots becoming southwest in the afternoon. Seas 2 to 3 feet. A chance of showers and thunderstorms.
Sunday Night...Southwest winds 5 to 10 knots becoming south after midnight. Seas 3 feet. A chance of showers and thunderstorms.
Monday...South winds around 5 knots. Seas 2 to 3 feet. A chance of showers and thunderstorms.
Have a great Friday Night & Saturday! God bless!
-DM-
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