1. Hurricane conditions, life-threatening storm surge, and heavyrainfall are expected from Marco along portions of the Gulf Coastbeginning on Monday, and Hurricane and Storm Surge Warnings havebeen issued. Interests in these areas should follow any advicegiven by local government officials.

2. Tropical Storm Laura could bring additional storm surge,rainfall, and wind impacts to portions of the U.S. Gulf Coast by themiddle of the week. This could result in a prolonged period ofhazardous weather for areas that may also be affected by Marco.Interests there should monitor the progress of Marco and Laura andupdates to the forecast during the next few days.

1. Hurricane conditions, life-threatening storm surge, and heavyrainfall are expected from Marco along portions of the Gulf Coastbeginning on Monday. Interests in these areas should follow any advice given by local government officials.

2. Tropical Storm Laura could bring additional storm surge,rainfall, and wind impacts to portions of the U.S. Gulf Coast by themiddle of the week. This could result in a prolonged period ofhazardous weather for areas that may also be affected by Marco.Interests there should monitor the progress of Marco and Laura andupdates to the forecast during the next few days.

CHANGES WITH THIS ADVISORY:

None.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Storm Surge Warning is in effect for....
- Morgan City Louisiana to Ocean Springs Mississippi
- Lake Borgne

A Hurricane Warning is in effect for...
- Morgan City Louisiana to the Mouth of the Pearl River

A Storm Surge Watch is in effect for...
- Sabine Pass to Morgan City Louisiana
- Ocean Springs Mississippi to the Mississippi/Alabama border
- Lake Pontchartrain and Lake Maurepas

A Hurricane Watch is in effect for...
- Intracoastal City Louisiana to west of Morgan City
- Lake Pontchartrain, Lake Maurepas, and Metropolitan New Orleans

A Tropical Storm Warning is in effect for...
- Mouth of the Pearl River to the Mississippi/Alabama border
- Lake Pontchartrain, Lake Maurepas, and Metropolitan New Orleans

A Tropical Storm Watch is in effect for...
- Mississippi/Alabama border to the Alabama/Florida border

A Storm Surge Warning means there is a danger of lifethreatening inundation, from rising water moving inland from the coastline, during the next 36 hours in the indicated locations. For a depiction of areas at risk, please see the National Weather Service Storm Surge Watch/Warning Graphic, available at hurricanes.gov. This is a lifethreatening situation. Persons located within these areas should take all necessary actions to protect life and property from rising water and the potential for other dangerous conditions. Promptly follow evacuation and other instructions from local officials.

A Hurricane Warning means that hurricane conditions are expected somewhere within the warning area. A warning is typically issued 36 hours before the anticipated first occurrence of tropicalstormforce winds, conditions that make outside preparations difficult or dangerous. Preparations to protect life and property should be rushed to completion.

A Storm Surge Watch means there is a possibility of life threatening inundation, from rising water moving inland from the coastline, in the indicated locations during the next 48 hours. For a depiction of areas at risk, please see the National Weather Service Storm Surge Watch/Warning Graphic, available at hurricanes.gov.

A Hurricane Watch means that hurricane conditions are possible within the watch area.

A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area within 36 hours.

A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, generally within 48 hours.

For storm information specific to your area in the United States, including possible inland watches and warnings, please monitor products issued by your local National Weather Service forecast office. For storm information specific to your area outside of the United States, please monitor products issued by your national meteorological service.

STORM SURGE: The combination of a dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline. The water could reach the following heights above ground somewhere in the indicated areas if the peak surge occurs at the time of high tide...

Morgan City LA to Ocean Springs MS including Lake Borgne...46 ft Sabine Pass to Morgan City LA...24 ft Ocean Springs MS to the MS/AL Border...24 ft Lake Pontchartrain and Lake Maurepas...24 ft MS/AL Border to AL/FL Border including Mobile Bay...13 ft

The deepest water will occur along the immediate coast in areas of onshore winds, where the surge will be accompanied by large and dangerous waves. Surgerelated flooding depends on the relative timing of the surge and the tidal cycle, and can vary greatly over short distances. For information specific to your area, please see products issued by your local National Weather Service forecast office.

WIND: Hurricane conditions are expected within the hurricane warning area by midday Monday, with tropical storm conditions possible by early Monday. Tropical storm conditions are possible within the tropical storm watch area on Monday, and hurricane conditions are possible within the hurricane watch areas late Monday.

RAINFALL: Marco is expected to produce rainfall accumulations of 2 to 4 inches with isolated maximum amounts of 6 inches across the Central U.S. Gulf coast through Tuesday.

This rainfall may result in isolated areas of flash and urban flooding along the Central U.S. Gulf Coast.

SURF: Swells generated by Marco are likely to affect portions of the northern Gulf Coast later today. These swells are likely to cause lifethreatening surf and rip current conditions. Please consult products from your local weather office.

TORNADOES: An isolated tornado will be possible early Monday morning near the southeast Louisiana coast.

At 100 PM CDT (1800 UTC), the center of Hurricane Marco was located near latitude 25.3 North, longitude 87.4 West. Marco is moving toward the northnorthwest near 14 mph (22 km/h), and this motion is expected to continue through tonight, followed by a turn toward the northwest by Monday. On the forecast track, Marco will cross the central Gulf of Mexico today and will approach southeastern Louisiana on Monday. A gradual turn toward the westnorthwest with a decrease in forward speed is expected after Marco moves inland.

Maximum sustained winds are near 75 mph (120 km/h) with higher gusts. Marco is expected to be a hurricane when it approaches the northern Gulf Coast on Monday. Rapid weakening is expected after Marco moves inland.

Hurricaneforce winds extend outward up to 20 miles (30 km) from the center and tropicalstormforce winds extend outward up to 100 miles (160 km) from the center.

The estimated minimum central pressure is 992 mb (29.29 inches).

Deep convection with cloud tops of -75 to -80 degrees C has persisted over the center of Marco for the past several hours. An Air Force Reserve Hurricane Hunter aircraft currently investigating the cyclone measured winds equivalent to 62 kt both with the SFMR and in a dropsonde in the northeastern eyewall. However, the aircraft reported peak 850-mb flight level winds of only 64 kt. Based on a blend of these data it appears that Marco is on the cusp of becoming a hurricane, but is not quite there yet. Therefore, the initial intensity remains 60 kt.

Based on the SHIPS guidance, Marco has about a 12-24 hour window to intensify in an environment characterized by moderate southwesterly shear, very warm waters, and plenty of atmospheric moisture. After that time, the vertical wind shear is expected to increase and this should begin to dominate the cyclone's environment. The latest NHC intensity forecast is unchanged from the previous one, forecasting Marco to become a hurricane later today, and maintaining hurricane intensity up until landfall in agreement with the latest LGEM intensity guidance. While it is possible that Marco will weaken just prior to landfall due to the increasing shear, there is little difference in the impacts between a 60 and 65 kt system.

Marco is moving north-northwestward or 340/12 kt. Although the overall guidance has not changed much since the previous advisory, there remains considerable spread in this guidance by the time Marco reaches the northern Gulf coast. This spread could be attributed to the varying ways the models handle the system as it encounters the more hostile environment near the coast. Since the track consensus aids have changed little through 36 h, the official forecast is essentially the same as the previous one through that time. The model guidance has shifted a little northward beyond 36 h, so the official forecast was nudged to the north during that time as well.

Shortly after the 10 AM CDT advisory was issued, the Air Force Reserve Hurricane Hunter aircraft investigating Marco measured SFMR winds of 65 to 69 kt for several minutes. A dropsonde around the same time also measured winds equivalent to 64 kt at the surface. Based on these data, it was evident that Marco had strengthened into a hurricane. Since that time, the convective pattern has changed little, and the final leg of the aircraft mission did not reveal any notable changes to the cyclone's intensity. Therefore, the initial intensity has been set to 65 kt, which is also in agreement with the latest Dvorak intensity estimate from SAB.

Marco continues to move north-northwest at around 11 kt. Model guidance is in good agreement on a north-northwest and then northwest motion into Monday morning as Marco nears the northern Gulf coast. However, there has been a major shift in the track guidance beyond Monday morning, and the majority of the forecast models now keep Marco offshore of the northern Gulf coast for the next few days rather than moving it inland over Louisiana Monday afternoon. Since this shift was so abrupt, I would rather split the difference between the previous official forecast track and the latest consensus tracks until another round of model runs can confirm this new suggested track is higher confidence. Based on this shift in track, tropical storm conditions are expected farther west along the Louisiana coast, and a Tropical Storm Warning has been issued from Morgan City to Cameron, Louisiana. It should be noted that if the trend in the models are correct, some of the impacts over portions of the north-central Gulf coast could be lessened.

The current shear analysis from UW-CIMSS shows that Marco is experiencing about 20-25 kt of southwesterly shear, yet Marco has been able to slowly strengthen in this environment today, likely due to the presence of very warm waters and plenty of atmospheric moisture. By late tonight and through Monday, the SHIPS guidance suggests this shear will increase to over 30 kt. This should limit any further intensification, and could cause Marco to weaken before it nears the northern Gulf coast Monday afternoon. By Monday night, the shear is forecast to increase to close to 40 kt, which should strip the convection away from the center of the cyclone, causing it to weaken. After 48 h, Marco is now expected to become a remnant low devoid of deep convection. The official NHC intensity forecast is similar to the previous one, but is at the high end of the guidance through 24 h.