The 4pm update was released from the NHC a bit ago, and it shows a reasonably dramatic shift in the forecasts for both Marco and Laura. The changes are likely prompted by the current interaction both are having with the atmosphere / topography around them and the new model data that is being enhanced by the Hurricane Hunter’s data.
The Hurricane Hunter data is likely a bigger influence. Better data means better forecasts.
The shift is in line with what I discussed in my post earlier today regarding Marco’s unlikely trek toward Texas and the “little dance” Marco and Laura would eventually do with each other.
Below is information directly from the National Hurricane Center with no filter.
Tropical Storm Marco
NHC FORECAST
MARCO STATS
LOCATION…18.0N 68.1W
ABOUT 100 MI…160 KM W OF PONCE PUERTO RICO
ABOUT 125 MI…200 KM ESE OF SANTO DOMINGO DOMINICAN REPUBLIC
MAXIMUM SUSTAINED WINDS…50 MPH…85 KM/H
PRESENT MOVEMENT…W OR 280 DEGREES AT 18 MPH…30 KM/H
MINIMUM CENTRAL PRESSURE…1004 MB…29.65 INCHES
ADVISORIES
A Storm Surge Watch has been issued from Sabine Pass eastward to the Alabama/Florida border, including Lake Pontchartrain, Lake Maurepas, Lake Borgne, and Mobile Bay.
A Hurricane Watch has been issued from Intracoastal City Louisiana eastward to the Mississippi/Alabama border, including Lake Pontchartrain, Lake Maurepas, and Metropolitan New Orleans.
A Tropical Storm Watch has been issued from the Mississippi/Alabama border eastward to the Alabama/Florida border.
The government of Mexico has discontinued the Tropical Storm Warning for the northeastern Yucatan coast.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT:
A Storm Surge Watch is in effect for…
* Sabine Pass to the Alabama/Florida border
* Lake Pontchartrain, Lake Maurepas, Lake Borgne, and Mobile Bay
A Hurricane Watch is in effect for…
* Intracoastal City Louisiana to the Mississippi/Alabama border
* Lake Pontchartrain, Lake Maurepas, and Metropolitan New Orleans
A Tropical Storm Warning is in effect for…
* Province of Pinar del Rio Cuba
A Tropical Storm Watch is in effect for…
* Mississippi/Alabama border to the Alabama/Florida border
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 watch is typically issued 48 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous.
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, please monitor products issued by your national meteorological service.
DISCUSSION
Cutting to the chase, there have been some big changes among the model guidance, and subsequently the NHC forecast, for Marco this afternoon. While at this point it’s a little speculative, the data collected by this morning’s NOAA G-IV flight in the environment around Marco and across the Gulf of Mexico may have played a key role in the significant eastward shift seen in nearly all the 12z models. This isn’t to say that the uncertainty in the eventual track has diminished. In fact, various ensemble members from some of the global models still show a potential risk to the coast anywhere from Texas to Alabama, and it’s entirely possible that the volatile shifts seen in the models could continue. That being said, the new NHC track forecast has been shifted significantly eastward and now shows the center of Marco reaching southeastern Louisiana in about 2 days, which is the scenario currently shown by the GFS, ECMWF, HCCA, Florida State Superensemble, and the TVCN multi-model consensus. After Marco reaches the coast, the western Atlantic ridge is expected to build westward and should cause the cyclone to move more slowly toward the west-northwest across southern portions of Louisiana.
As far as the intensity is concerned, the last fix made by this morning’s reconnaissance flight indicated that the pressure had leveled off, and no higher winds had been observed from what was measured earlier in the flight. The radar presentation from Cuban radar has also degraded a bit, so Marco’s initial intensity is held at 55 kt. Marco is beginning to move into a zone of moderate southwesterly shear, but otherwise favorable conditions of warm ocean water and some upper-level divergence are expected to foster strengthening during the next day or so. With the exception of the HWRF, the other intensity models show Marco reaching hurricane strength, and the NHC foreast continues to show that possibility while Marco moves over the central Gulf. The shear is still expected to strengthen in 36-48 hours when the system is approaching the northern Gulf Coast, but with the shift in the forecast track, now there may not be enough time for Marco to weaken below hurricane intensity before it reaches land. The new NHC intensity forecast is near or just above the HCCA and Florida State Superensemble models and holds Marco as a hurricane until it reaches the coast.
The forecast track changes now bring tropical storm force winds to the coast in 36-48 hours, which necessitates the issuance of Hurricane and Storm Surge Watches for a portion of the northern Gulf Coast. These watches will likely need to be upgraded to warnings later tonight.
KEY MESSAGES
1. Tropical storm conditions will continue over portions of extreme western Cuba through this evening. Heavy rainfall is also expected in the eastern portions of the Mexican states of Quintana Roo and Yucatan, and across far western Cuba, which could result in flash flooding.
2. Marco is expected to approach the central Gulf Coast as a hurricane on Monday. Hurricane conditions, life-threatening storm surge, and heavy rainfall are possible along portions of the Gulf Coast beginning on Monday, and Hurricane and Storm Surge watches have been issued. Interests in these areas should follow any advice given by local government officials.
3. Tropical Storm Laura could bring additional storm surge, rainfall, and wind impacts to portions of the U.S. Gulf Coast by the middle of next week. This could result in a prolonged period of hazardous weather for areas that could be affected by Marco. Interests there should monitor the progress of Marco and Laura and updates to the forecast during the next few days.
FORECAST POSITIONS AND MAX WINDS
INIT 22/2100Z 21.9N 85.7W 55 KT 65 MPH
12H 23/0600Z 23.3N 86.5W 65 KT 75 MPH
24H 23/1800Z 25.3N 87.3W 75 KT 85 MPH
36H 24/0600Z 27.5N 88.3W 75 KT 85 MPH
48H 24/1800Z 29.3N 89.6W 65 KT 75 MPH…ON THE COAST
60H 25/0600Z 30.4N 91.1W 50 KT 60 MPH…INLAND
72H 25/1800Z 31.1N 92.7W 40 KT 45 MPH…INLAND
96H 26/1800Z 32.3N 95.6W 25 KT 30 MPH…INLAND
120H 27/1800Z…DISSIPATED
Tropical Storm Laura
NHC FORECAST
LAURA STATS
LOCATION…18.0N 68.1W
ABOUT 100 MI…160 KM W OF PONCE PUERTO RICO
ABOUT 125 MI…200 KM ESE OF SANTO DOMINGO DOMINICAN REPUBLIC
MAXIMUM SUSTAINED WINDS…50 MPH…85 KM/H
PRESENT MOVEMENT…W OR 280 DEGREES AT 18 MPH…30 KM/H
MINIMUM CENTRAL PRESSURE…1004 MB…29.65 INCHES
ADVISORIES
A Tropical Storm Watch has been issued for the Florida Keys from Ocean Reef to Key West and for the Dry Tortugas, including Florida Bay.
The government of Cuba has issued a Tropical Storm Warning for the Cuban provinces of Camaguey, Las Tunas, Holguin, Guantanamo, Santiago de Cuba, and Granma.
The government of the Bahamas has issued a Tropical Storm Watch for Andros Island.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT:
A Tropical Storm Warning is in effect for…
* Puerto Rico, Vieques and Culebra
* U.S. Virgin Islands
* The northern coast of the Dominican Republic from Cabo Engano to the border with Haiti
* The southern coast of the Dominican Republic from Cabo Engano to Punta Palenque
* The northern coast of Haiti from Le Mole St. Nicholas to the border with the Dominican Republic
* The southeastern Bahamas and the Turks and Caicos Islands
* Cuban provinces of Camaguey, Las Tunas, Holguin, Guantanamo, Santiago de Cuba, and Granma
A Tropical Storm Watch is in effect for…
* The central Bahamas
* Andros Island
* Florida Keys from Ocean Reef to Key West and the Dry Tortugas
* Florida Bay
A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area.
A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, generally within 48 hours.
Interests elsewhere in Cuba should monitor the progress of Laura. Additional tropical storm watches or warnings may be needed there
tonight.
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.
DISCUSSION
A couple of hours ago an observing site on the southeast coast of Puerto Rico, Las Mareas, reported sustained winds of 52 kt. These winds were apparently associated with a mesocyclone embedded within the larger-scale circulation and not representative of the intensity of the tropical storm. Scatterometer data and WSR-88D Doppler velocities from San Juan support an intensity of 45 kt. Since the center should be moving over land for the next 48 hours or so, no additional intensification is anticipated until Monday night when the center moves over the southeastern Gulf of Mexico. Over warm waters, with anticipated weak vertical shear, and anticyclonic flow aloft, Laura will likely strengthen into a hurricane before it reaches the northern Gulf of Mexico coast. The NHC intensity forecast is close to the multi-model consensus, but given the possibility of a favorable upper-air environment over the Gulf, this forecast could be conservative. At this time it does not seem likely that Marco, which is forecast to make landfall on the north-central Gulf coast a day or two earlier than Laura, should have much of an influence on the latter system.
Center locations from earlier scatterometer data, low-cloud motions, and Dvorak fixes from both TAFB and SAB, give a motion of about
280/16 kt. Laura should move west-northwestward along the southern side of a mid-tropospheric anticyclone centered near the southeastern U.S. coast through 72 hours. Then, the cyclone is expected to turn northwestward to northward on the western side of the high. The official track forecast is on the right side of the track guidance suite.
Given the predicted track and wind radii, a Tropical Storm Watch has been issued for the Florida Keys and the Dry Tortugas.
KEY MESSAGES
1. Tropical storm conditions are expected to continue across portions of the U.S. Virgin Islands and Puerto Rico through this evening. Tropical storm conditions are also expected across portions of the Dominican Republic and Haiti, the Turks and Caicos, the southeastern Bahamas, and central and eastern Cuba through Sunday. Heavy rainfall is likely across these areas and could cause mudslides and flash and urban flooding through Sunday, with widespread river flooding possible in Puerto Rico.
2. Tropical storm conditions are possible over portions of the central Bahamas and Andros Island Sunday night and Monday, and in the Florida Keys on Monday.
3. The details of the long-range track and intensity forecasts remain uncertain since Laura is forecast to move near or over portions of the Greater Antilles through Monday. However, Laura is forecast to strengthen over the Gulf of Mexico and could bring storm surge, rainfall, and wind impacts to portions of the U.S. Gulf Coast by the middle of next week. This could result in a prolonged period of hazardous weather for areas that are likely to be affected by Tropical Storm Marco earlier in the week. Interests there should monitor the progress of Laura and Marco and updates to the forecast during the next few days.
FORECAST POSITIONS AND MAX WINDS
INIT 22/2100Z 18.0N 68.1W 45 KT 50 MPH
12H 23/0600Z 18.9N 70.6W 45 KT 50 MPH…INLAND
24H 23/1800Z 20.1N 74.3W 45 KT 50 MPH…INLAND
36H 24/0600Z 21.6N 78.1W 45 KT 50 MPH…INLAND
48H 24/1800Z 23.0N 81.6W 45 KT 50 MPH…INLAND
60H 25/0600Z 24.3N 84.5W 55 KT 65 MPH…OVER WATER
72H 25/1800Z 25.7N 87.3W 65 KT 75 MPH
96H 26/1800Z 29.0N 90.7W 75 KT 85 MPH
120H 27/1800Z 33.0N 91.0W 30 KT 35 MPH…INLAND
