Tropical weather analysis - October 22, 2010

Richard

Tropical Storm Richard is slowly intensifying. As of the most recent NHC advisory, here is the latest information on Richard:

Wind: 45 mph, with higher gusts
Movement: W at 5 mph
Pressure: 1005 mb
Location: 16.2°N 81.7°W
Category: Tropical storm

Visible satellite animations suggest that the center is located underneath the mass of deep convection, but the imagery also suggests some vertical shearing over the system. However, there are some indications that this shear is lessening. Additionally, Richard's cyclonic circulation appears to be wrapping some stratocumulus clouds into the western semicircle. Indeed, the latest run of the SHIPS model places 700-500 mb relative humidity values at only 59%, suggesting a very dry mid-level airmass. Finally, Richard's overall circulation envelope appears to be a bit elongated, as evidenced by low-cloud motions observed on satellite imagery. These factors should prevent any rapid intensification of Richard for now.

The dry air and shear notwithstanding, Richard certainly has the potential to become a formidable hurricane over the next several days, as upper-level winds are forecast to be quite favorable for intensification. There are also some indications on water vapor imagery that the very dry airmass is gradually moistening, and high cloud motions derived from satellite imagery imply a lessening of the aforementioned vertical shear.

I expect continued slow intensification of Richard over the next 18 hours, with a more steady rate of strengthening thereafter. However, the potential certainly exists for Richard to rapidly intensify beyond that time, given the very high oceanic heat content located across the western Caribbean Sea, and the light vertical shear profiles forecast.

I expect that by 24 hours, Richard will have become a hurricane.

Richard is currently located in a col region between a developing anticyclone across the Gulf of Mexico and a very potent longwave trough over the western and central Atlantic. This synoptic scale setup indicates that Richard will move only slowly in the short-term. Some erratic motion cannot be ruled out, as well.

Models are split into two camps: the first set, comprised of the CMC, NOGAPS, and UKMET forecast a much weaker Richard. As a result, a shortwave trough and associated cold front that is forecast by the models to branch off from the base of a longwave trough over the high plains/upper midwest in about three days has little appreciable effect on the cyclone. Should this scenario verify, Richard would move into Central America in about two to three days, and eventually into northeast Mexico or south Texas. In fact, the CMC and NOGAPS even lose Richard's circulation over the rugged terrain of Central America.

The latter set of models, comprised of the GFS, HWRF, GFDL, and ECMWF, forecast a deeper, more vertically respectable Richard to respond more significantly to the trough. As a result, these models have Richard turning NW to NNW in about four days toward a developing weakness in the ridge due to a southward movement of said trough toward the Gulf Coast states. In this scenario, Richard would expected to be in the eastern Bay of Campeche in the Gulf of Mexico at that time.

Given current trends, which suggests slow organization (but Richard is still undoubtedly struggling), as well as the forecast of an improving upper wind and thermodynamic environment, which appears to be happening as we speak, I will side with the latter camp.

This track tends to agree pretty well with the NHC's current one, although I am a bit farther to the east of their forecast track at days four and five.

Richard does not pose a significant threat to the United States, as vertical shear profiles are forecast to be quite unfavorable across the Gulf of Mexico. In fact, dissipation of Richard well before "landfall" can be expected. However, Central America and the Yucatan Peninsula may not be so fortunate. The GFDL brings Richard up to Category 4 strength before it slams it into northeastern Belize in about 66-72 hours.

Interests in Honduras, Belize, the Yucatan Peninsula should closely follow the progress of this system over the next several days. Richard could also pose a long-range rainfall threat for from the central Texas to southwest Louisiana coasts, and interests in those areas should also follow the progress of Richard over the next few days.

Again, I want to reiterate that the US is unlikely to see anything more than a little bit of rain from Richard's remnants. Richard will NOT be an organized tropical system by the time it reaches any of the aforementioned areas. However, the rainfall could be locally heavy depending on how moist the environment gets with the approach of said cold front. Tropical systems are notorious for entraining moisture into approaching cold fronts, which can in turn create some serious rainfall and associated flood potential.

Since these areas are in a drought though, the rainfall is unlikely to cause significant flooding problems for Texas and Louisiana.

The most likely target for Richard's Central American landfall is Belize, and for its US landfall, western Louisiana, near Cameron.

Watches and warnings

A HURRICANE WATCH IS IN EFFECT FOR...
* HONDURAS FROM THE NICARAGUA/HONDURAS BORDER WESTWARD TO LIMON AND
THE BAY ISLANDS
* EAST COAST OF MEXICO FROM PUNTA GRUESA TO CHETUMAL

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* HONDURAS FROM THE NICARAGUA/HONDURAS BORDER WESTWARD TO LIMON AND
THE BAY ISLANDS

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* HONDURAS FROM WEST OF LIMON TO THE GUATEMALA BORDER.
* BELIZE

Invest 90L

A strong tropical wave is located near the Cape Verde Islands. This wave has been dubbed "Invest 90L" by the National Hurricane Center. The associated shower activity has become a little better organized, but upper-level winds are only marginally conducive for development, and a less favorable upper wind environment is forecast over the next 12-24 hours. Indeed, southwesterly shear is rapidly approaching the system.

This system does not pose a threat to any land areas, and can be expected to move NW to NNW throughout the forecast period.

Elsewhere

Elsewhere in the tropics, the GFS and ECMWF are indicating that tropical cyclogenesis might occur in the eastern Caribbean in about 7-10 days. This could occur as the ITCZ lifts northward with the approach of the upward MJO.

Since the GFS has been particularly fluent in sniffing out long-range storms this year, I would not discount this possibility at all. However, upper-level winds will not be particularly favorable for development over that part of the Caribbean, so no significant intensification should be expected if this system does form.