It appears from satellite imagery that vertical wind shear quickly weakened Hurricane Carlos on Tuesday night.  At 11:00 p.m. EDT on Tuesday the center of Hurricane Carlos was located at latitude 18.2°N and longitude 104.5°W which put it about 55 miles (90 km) south-southwest of Manzanillo, Mexico.  Carlos was moving toward the northwest at 5 m.p.h. (7 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 988 mb.  A Hurricane Watch was in effect for the portion of the coast from Playa Perula to Punta San Telmo, Mexico and a Tropical Storm Warning was in effect for the portion of the coast from Cabo Corrientes to Punta San Telmo, Mexico.

After intensifying on Tuesday afternoon and exhibiting well developed upper level divergence, the structure of Hurricane Carlos degenerated quickly on Tuesday night.  Most of the strong thunderstorms dissipated.  Satellite imagery showed an exposed low level center near the Mexican coast, while the upper level canopy was moving westward away from the low level center.  The decoupling of the upper and low parts of the circulation, usually leads to quick weakening of a hurricane.  The small size of Carlos could allow it to weaken even more quickly than an average hurricane.  The most recent satellite images showed a few thunderstorms forming south of the center of circulation.  However, wind shear caused by an upper level ridge north of Carlos may be too strong to allow for the system to regain its vertical integrity.  Tropical cyclones that are sheared apart sometimes have one chance to redevelop.  The low level center is moving closer to the coast of Mexico and interaction with land may prevent any chance for redevelopment.

If the low level center remains separated from the rest of the system and it does not extend higher into the atmosphere, it will be steered by the winds in the lower levels.  Those winds appear to be taking it north-northwest toward the coast.  Carlos could dissipate quickly if it makes landfall, or the circulation could linger for a day or two if it stays farther offshore.

Hurricane Carlos has a very small circulation and the tropical storm force winds extend out less than 50 miles (80 km) from the center.  At 8:00 p.m. EDT on Monday the center of Hurricane Carlos was located at latitude 17.2°N and longitude 103.3°W which put it about 90 miles (145 km) southwest of Lazaro Cardenas, Mexico and about 140 miles (225 km) south-southeast of Manzanillo.  Carlos was moving toward the west-northwest at 6 m.p.h. (9 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 989 mb.  A Hurricane Watch and a Tropical Storm Warning is in effect for the portion of the coast from Playa Perula to Punta San Telmo.

The small circulation of Hurricane Carlos continues to move over the Pacific Ocean west of Mexico.  It is moving over water where the Sea Surface Temperature is about 29°C.  An upper level ridge north of the hurricane is generating northeasterly winds that are impinging on the northern side of Carlos.  Those winds are inhibiting upper level divergence from the northern side of Carlos.  The small circulation means than any thunderstorms form near the center and the strongest storms are south of the center.  The small circulation also means that wind shear can have a very big effect on Carlos.  Even moderate winds in the upper levels would be strong enough to disrupt the vertical coherence of the hurricane and blow away the upper part of Carlos.  The vertical wind shear is expected to be modest in the short term, and Carlos is forecast to maintain its intensity for a day or two.  However, it would not take much increase in the wind shear to blow the top off Carlos.

The upper level ridge is expected to continue to steer Carlos toward the west-northwest for 24 to 36 hours.  After that time two scenarios are possible.  In one scenario the upper level ridge weakens and Carlos turns northward and moves very close the coast of Mexico near Cabo Corientes.  In an alternative scenario the ridge maintains its intensity and it steers Carlos toward the west-northwest for the next few days.  A third scenario, which could occur at any time, would happen if wind shear blows the top off of Carlos.  In that case the surface circulation would be steered westward by the lower level flow until it dissipated.  These three possible scenarios make the future track of Carlos very uncertain.

Carlos weakened to a tropical storm as it moved west of Acapulco, Mexico on Sunday.  At 11:00 p.m. EDT on Sunday the center of Tropical Storm Carlos was located at latitude 16.7°N and longitude 101.3°W which put it about 95 miles (150 km) west of Acapulco and about 110 miles (175 km) southeast of Lazaro Cardenas.  Carlos was moving toward the northwest at 6 m.p.h. (9 km/h).  The maximum sustained wind speed was 70 m.p.h. (110 km/h) and there were wind gusts to 85 m.p.h. (135 km/h).  The minimum surface pressure was 998 mb.  Carlos is a small tropical cyclone.  The tropical storm force winds only extend out about 50 miles (80 km) from the center and it has a Hurricane Size Index (HSI) of 1.7.  The government of Mexico has issued a Hurricane Warning for the portion of the coast that extends from Punta San Telmo to Tecpan de Galeana.  A Hurricane Watch has been issued for the portion of the coast from Playa Perula to Punta San Telmo.

Carlos was nearly stationary for several days and its winds mixed cooler water to the surface.  In addition the circulation pulled in drier air from Mexico as it got closer to the coast.  The combined effects of cooler water and drier resulted in less energy to drive the circulation and Carlos weakened to a tropical storm on Sunday.  Late in the day it started to move toward the northwest and get away from the cooler water.  Carlos is moving over an area where the Sea Surface Temperature (SST) is near 30°C.  Recent satellite images indicate that stronger thunderstorms are forming near the center of circulation.  The flow around Carlos is still pulling in drier air from Mexico and there are fewer thunderstorms in the northern half of the tropical storm.  The small size of Carlos means that it can strengthen or weaken more quickly than a larger storm because there is less mass to accelerate.  The upper level winds over Carlos have lessened and there is not as much vertical wind shear.  If Carlos remains over water, it is likely to intensify back to a hurricane on Monday.

An upper level ridge over Mexico is moving slowly toward the east and it is starting to steer Carlos toward the northwest.  The ridge is expected to continue to steer the tropical storm toward the northwest or west-northwest on Monday.  As Carlos approaches the western end of the ridge is expected to turn more toward the west-northwest.  There is some uncertainty about where the turn will occur.  Guidance from some models have Carlos turning farther east and making a landfall between Manzanillo and Cabo Corientes, while some other models have the tropical storm moving farther west before turning.  Either scenario is plausible and hence, the high degree of uncertainty about the future track of Carlos.

An eye developed in the center of Carlos and the National Hurricane Center upgraded it to a hurricane.  At 5:00 p.m. EDT on Saturday the center of Hurricane Carlos was located at latitude 15.2°N and longitude 100.0°W which put it about 120 miles (190 km) south of Acapulco, Mexico and about 240 miles (390 km) southeast of Lazaro Cardenas, Mexico.  Carlos was moving toward the north at 2 m.p.h. (4 km/h).  The maximum sustained wind speed was 85 m.p.h. (140 km/h) and there were gusts to 105 m.p.h. (170 km/h).  The minimum surface pressure was 986 mb.  The Hurricane Intensity Index (HII) is 12.7.  The Hurricane Size Index (HSI) is 10.3.  The Hurricane Wind Intensity Size Index (HWISI) is 23.0.  These indices suggest that Carlos is capable of producing regional serious wind damage.  The government of Mexico has issued a Hurricane Warning for the portion of the coast from Lazaro Cardenas to Tucpan de Galeana.  A Hurricane Watch is in effect for the portion of the coast from Punta San Telmo to Lazaro Cardenas.  A Tropical Storm Warning has been issued for the portion of the coast from Tecpan de Galeana to Punta Maldonado.

The circulation near the center of Carlos is more well organized than it was 12 hours ago and an eye is clearly apparent on visible satellite imagery.  The hurricane appears to still be pulling in some drier air from Mexico because there is a gap on the northern side of the eyewall.  However, the drier air is less of a factor than it was on Friday.  Carlos is over water where the Sea Surface Temperature (SST) is near 30°C.  At some point it’s lack of movement will cause its winds to mix cooler water to the surface but that has not happened yet.  An upper level ridge located to the north of Carlos is generating some easterly winds near the top of the hurricane, but upper level divergence has increased since yesterday.  The upper level divergence is pumping out mass, which is allowing the surface pressure to decrease and Carlos to strengthen.  Drier air and modest vertical wind shear will slow the intensification of Carlos, but the hurricane should get stronger in the short term while it remains over warm SSTs.

A combination of the upper level ridge north of Carlos and an upper low over the Gulf of Mexico is creating a zone of weak steering winds near Carlos, which is why it has moved so little.  Later this weekend the upper level low is forecast to move away and the ridge will move northeast of the hurricane.  The change in position will cause Carlos to move toward the northwest.  Most of the guidance from numerical models keep the center of Carlos west of the coast of Mexico, but some models are now bringing it much closer to land.  The change in the guidance prompted the issuance of new watches and warnings for portions of the Mexican coast.

Tropical Storm Carlos moved very little on Friday.  At 5:00 p.m. EDT on Friday the center of Tropical Storm Carlos was located at latitude 14.7°N and longitude 100.6°W which put it about 160 miles (255 km) south-southwest of Acapulco and about 250 miles (405 km) south-southeast of Lazaro Cardenas, Mexico.  Carlos was stationary.  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were gusts to 70 m.p.h. (115 km/h).  The minimum surface pressure was 997 mb.

The intensity of Carlos changed little on Friday and the organization of the circulation fluctuated during the day.  The core of the circulation exhibited greater organization during the afternoon when more thunderstorms developed near the center.  Carlos remains over water where the Sea Surface Temperature (SST) is near 30°C.  At times it appears as though Carlos may be pulling in some sinking drier air from Mexico, because most of the thunderstorms are developing in the southern portion of the circulation.  An upper level ridge north of Carlos is generating some northeasterly winds that are affecting the outflow on the northern side of the tropical storm.  However, an upper level low over the Gulf of Mexico may be enhancing some upper level divergence on the eastern side of the storm.  If Carlos were to remain stationary for several more days, its winds would mix up cooler water.  Carlos should not have as big an effect on the SSTs as Blanca did when it was stationary, because Carlos is weaker than Blanca was.  The intensity forecast is highly uncertain because the SSTs are favorable for intensification, but drier air and vertical wind shear would tend to inhibit strengthening.  The most likely outcome is modest intensification during the weekend.

The interaction of the upper ridge over Mexico and the upper low over the Gulf of Mexico is creating a zone of weak steering winds near Carlos, which is the reason it has been stationary.  Eventually, during the weekend, the upper ridge is expected to move eastward and begin to steer Carlos toward the northwest.  On its anticipated track the center of Carlos is expected to remain off the coast of Mexico, but it is expected to move parallel to the coast.  Any deviation of the track to the east could bring the center very near the coast of Mexico.