I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.
By: KoritheMan , 7:42 AM GMT on September 14, 2012
Tropical Storm Nadine continues to move across the central Atlantic Ocean. As of the latest NHC advisory, the following information was available on the tropical cyclone:
Wind: 70 mph, with higher gusts
Location: 25.0°N 53.7°W
Movement: NNW at 15 mph
Pressure: 989 mb
Satellite fixes suggest little change to Nadine. A 0000 UTC AMSUB overpass indicated that the center was a little to the southwest of the central dense overcast, symptomatic of southwesterly shear, as diagnosed by UW-CIMSS and the SHIPS model.
Figure 1. Latest infrared satellite image of Tropical Storm Nadine. Image credit: NOAA
Interestingly, the outflow pattern is still quite marked on satellite images, which suggests that the majority of the shear is confined below the outflow level.
The GFS shows the shear decreasing in about 24-36 hours. The SHIPS takes Nadine to hurricane strength in 36 hours, but curiously still shows shear. Either way, the tropical cyclone is moving away from the upper low northeast of Puerto Rico. As this happens, the upper tropospheric flow over Nadine should veer from southwesterly to southeasterly, which is a pattern more conducive to intensification. The HWRF makes Nadine a major hurricane in about three days, but the remainder of the intensity models are well below that value. Additionally, the HWRF seems to overdo the intensity of tropical cyclones quite often.
Since most of the guidance makes Nadine a hurricane in what appears to be a favorable environment on the GFS, I will do the same. Beyond day three, sea surface temperatures should decrease, which is expected to induce a slow weakening of Nadine at longer ranges.
Water vapor imagery shows that Nadine is about to round the western periphery of the subtropical ridge over the central Atlantic, although for now a more north-northwest continues. In about 6-12 hours, Nadine is expected to turn northward, then gradually turn toward the east-northeast as the cyclone becomes embedded in high latitude flow north of the subtropical ridge axis. The global models are in good agreement on this, although there are still some differences, albeit less substantial, in regards to where Nadine ends up at longer ranges. But since the GFS and ECMWF have come into better agreement, I will tend to follow them instead of the generally less reliable models. My forecast is pretty similar to the National Hurricane Center one, albeit slower at day five due to the models unanimously slowing the forward speed.
5-day intensity forecast
INITIAL 09/14 0600Z 60 KT 70 MPH
12 hour 09/14 1800Z 60 KT 70 MPH
24 hour 09/15 0600Z 65 KT 75 MPH
36 hour 09/15 1800Z 65 KT 75 MPH
48 hour 09/16 0600Z 70 KT 80 MPH
72 hour 09/17 0600Z 75 KT 85 MPH
96 hour 09/18 0600Z 75 KT 85 MPH
120 hour 09/19 0600Z 70 KT 80 MPH
5-day track forecast
Figure 2. My 5-day forecast track for Nadine.
Tropical Storm Kristy continues to march across the Pacific well south of Baja. As of the latest NHC advisory, the following was posted on the storm:
Wind: 50 mph, with higher gusts
Location: 19.7°N 111.1°W
Movement: WNW at 10 mph
Pressure: 1000 mb
Earlier microwave data suggested that the center was still to the north of the convection, but recent satellite images indicate that Kristy may be making a bit of a comeback. However, the convection remains pretty asymmetric.
Figure 3. Latest infrared satellite image of Tropical Storm Kristy. Image credit: NOAA
While the shear is forecast to decrease -- in fact it may be doing so now -- this will be concurrent with passage over cooler waters. Indeed, analysis of water temperatures in the region suggests that Kristy will cross the 26C isotherm in about 12 hours. Thus, the current resurgence of convection is very likely to be temporary, and was probably aided by diurnal processes. Kristy is expected to become a remnant low in about three days, possibly sooner.
Kristy is moving toward a break in the Pacific subtropical high as a trough amplifies offshore the western United States, which should cause a bend toward the northwest, or at least ocntinue the west-northwest motion. In about three days, Kristy is expected to slow and turn north then east as a decaying remnant low.
5-day intensity forecast
INITIAL 09/14 0600Z 45 KT 50 MPH
12 hour 09/14 1800Z 45 KT 50 MPH
24 hour 09/15 0600Z 40 KT 45 MPH
36 hour 09/15 1800Z 40 KT 45 MPH
48 hour 09/16 0600Z 35 KT 40 MPH
72 hour 09/17 0600Z 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
96 hour 09/18 0600Z 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
120 hour 09/19 0600Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
5-day track forecast
Figure 4. My 5-day forecast track for Kristy.
An area of disturbed weather located several hundred miles southwest of Tropical Storm Kristy is producing disorganized showers and thunderstorms. The system is experiencing some northeasterly shear, but this should steadily abate. Upper-level winds favor additional development, although the GFS thinks the flow will be more diffluent than anticyclonic.
This low is expected to move generally westward over the next few days.
Probability of development in 48 hours: 50%
A second area of disturbed weather is located west of disturbance 91E, around 130W. While upper-level winds are fairly light at the moment, water vapor imagery shows southwesterly shear approaching the system. The GFS repsonds to this by increasing the upper flow over the system over the next few days. I do not expect significant development from this area.
Probability of development in 48 hours: 20%
Comments will take a few seconds to appear.