Tropical Storm Kirk

Tropical Storm Kirk Track 1700 Hours September 23 2018
Tropical Storm Kirk Track 1700 Hours September 23 2018

NWS National Hurricane Center Miami FL 500 PM AST Sun Sep 23 2018

Tropical Storm Kirk’s (see 3 videos below) deep convection has diminished near the estimated center of Kirk, and the main thunderstorm activity is occurring over the northwestern and western peripheries of the circulation. This has the appearance of an arc cloud, suggesting that some drier mid-level air has been entrained into the tropical cyclone. Since the system should be moving over warmer waters and through low vertical shear for the next day or so, some strengthening is anticipated into early this weak. Later in the forecast period, Kirk should be encountering increasing shear associated with strong upper-level westerlies over the Caribbean, and this will likely cause weakening. The official forecast is close to the latest Florida State University Superensemble prediction and is the same as the previous NHC forecast.

Based on the latest center fixes, the motion continues swiftly toward the west, or about 280/20 kt. A mid-level subtropical ridge to the north of Kirk should steer the tropical cyclone westward at a fairly fast clip for the next couple of days. By days 3-4, the ridge weakens a bit and Kirk should slow its forward motion somewhat. The official track forecast has not changed much from the previous advisory and is close to the latest corrected consensus model, HCCA, prediction.

FORECAST POSITIONS AND MAX WINDS

INIT  23/2100Z  9.5N  32.3W   35 KT  40 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 12H  24/0600Z  9.9N  35.3W   40 KT  45 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 24H  24/1800Z 10.2N  39.5W   45 KT  50 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 36H  25/0600Z 10.4N  43.4W   50 KT  60 MPH - Tropical Storm (ESE Bridgetown, Barbados)
 48H  25/1800Z 10.6N  47.1W   50 KT  60 MPH - Tropical Storm (ESE Bridgetown, Barbados)
 72H  26/1800Z 11.6N  53.4W   45 KT  50 MPH - Tropical Storm (ESE Bridgetown, Barbados)
 96H  27/1800Z 12.9N  58.1W   40 KT  45 MPH - Tropical Storm (ESE Bridgetown, Barbados)
120H  28/1800Z 14.0N  63.0W   35 KT  40 MPH - Tropical Storm (WNW Castries, St. Lucia)

NWS National Hurricane Center Miami FL 1100 AM AST Sun Sep 23 2018

Tropical Storm Kirk’s cloud pattern has a figure 6 configuration, with most of the deep convective bands over the western semicircle of the circulation. Microwave imagery indicates that the center is near the eastern side of the main area of deep convection, as before. Dvorak classifications from both TAFB and SAB support keeping the intensity at 35 kt. The storm will be moving over warmer waters with fairly low shear for the next day or two, so some strengthening is anticipated in the short term. Later in the forecast period, increasing westerly shear should cause weakening. The official intensity forecast is similar to the model consensus through 48 hours, and follows the trends shown by the ECMWF and GFS global guidance thereafter. The latter models suggest that Kirk could open up into a trough when it nears the Caribbean.

Center fixes indicate that Kirk has been accelerating westward and the initial motion estimate is now 280/18 kt. A well-defined mid-level ridge to the north of the cyclone should cause an even faster westward motion over the next few days. Near the end of the forecast period, a weakness in the ridge is likely to lead to a slowing of the forward speed. The official forecast is a blend of the latest simple and corrected model consensus forecast tracks and is also similar to the previous NHC track.

FORECAST POSITIONS AND MAX WINDS

INIT  23/1500Z  9.3N  30.2W   35 KT  40 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 12H  24/0000Z  9.8N  33.2W   40 KT  45 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 24H  24/1200Z 10.2N  37.3W   45 KT  50 MPH - Tropical Storm (ESE Bridgetown, Barbados)
 36H  25/0000Z 10.5N  41.5W   50 KT  60 MPH - Tropical Storm (ESE Bridgetown, Barbados)
 48H  25/1200Z 10.7N  45.6W   50 KT  60 MPH - Tropical Storm (ESE Bridgetown, Barbados)
 72H  26/1200Z 11.2N  52.4W   45 KT  50 MPH - Tropical Storm (ESE Bridgetown, Barbados)
 96H  27/1200Z 12.3N  57.5W   40 KT  45 MPH - Tropical Storm (ESE Bridgetown, Barbados)
120H  28/1200Z 13.5N  62.0W   35 KT  40 MPH - Tropical Storm (ESE Bridgetown, Barbados)

NWS National Hurricane Center Miami FL 500 PM AST Sat Sep 22 2018

The convection associated with Tropical Storm Kirk  is currently disorganized, with the majority of it in a cluster to the west of the center. Most of the subjective and objective satellite intensity estimates are in the 30-35 kt range, so the initial intensity remains 35 kt for this advisory.

The forecast track takes Kirk over SSTs around 27C for the next 36 h or so with generally low shear, which appears favorable for gradual strengthening. However, there is a possibility that entrainment of dry air from an area of African dust present to the north of Kirk may allow less intensification than currently forecast. From 36-72 h, there is some divergence in the intensity guidance between the SHIPS and LGEM models, which forecast strengthening into a hurricane, and the dynamical models, which forecast little additional strengthening. The intensity forecast leans toward the dynamical models during that period. After 72 h, Kirk should encounter increasing westerly shear and gradually weaken. The intensity forecast, which is unchanged from the previous forecast, lies a little above the intensity consensus IVCN.

The initial motion is now 290/13. The subtropical ridge to the north of the storm should steer Kirk quickly westward for the next 72 h or so, with forward speeds reaching 20-25 kt. Later in the forecast period, Kirk should turn west-northwestward with a decrease in forward speed as it nears a developing weakness in the ridge near and to the east of the Lesser Antilles. The new forecast track, which is closest to the HCCA consensus model, is shifted a little to the north of the previous track. However, it continues to lie on the south side of the guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT  22/2100Z  8.6N  24.8W   35 KT  40 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 12H  23/0600Z  9.1N  27.1W   40 KT  45 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 24H  23/1800Z  9.5N  31.2W   45 KT  50 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 36H  24/0600Z  9.7N  35.7W   50 KT  60 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 48H  24/1800Z  9.8N  40.2W   50 KT  60 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 72H  25/1800Z 10.5N  48.0W   50 KT  60 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 96H  26/1800Z 11.5N  54.0W   45 KT  50 MPH - Tropical Storm (ESE Bridgetown, Barbados)
120H  27/1800Z 13.0N  59.0W   40 KT  45 MPH - Tropical Storm (ESE Bridgetown, Barbados)

NWS National Hurricane Center Miami FL 1100 AM AST Sat Sep 22 2018

The area of low pressure located well south of the Cabo Verde Islands now has a well-defined center and enough organized deep convection to be considered a tropical cyclone. The initial intensity is set to 35 kt based on data from recent ASCAT passes that showed an area of 30-35 kt winds northwest of the center.

Tropical Storm Kirk will be moving over SSTs around 27C for the next 36 hours or so with generally low shear, which should allow for some gradual strengthening. After that time, the SSTs increase quickly along the forecast track, but the SHIPS model and global model fields show the vertical shear increasing, in part due to the very fast low-level easterly flow. In addition, the GFS and ECMWF global models don’t show much development of the cyclone during the forecast period. As a result of these factors, little change in strength is forecast after 48 hours. The NHC forecast is close to the HCCA consensus aid through 48 hours and is near IVCN afterward.

The initial motion estimate is 280/12, but has the usual uncertainty for a system in the early stages of development. The cyclone is expected to be steered very quickly westward at low latitudes with forward speeds reaching 20-25 kt over the next 72 hours to the south of a mid-level ridge. Late in the period, some gain in latitude and a slight decrease in forward speed are shown as a weakness in the ridge develops to the east of the Lesser Antilles. The initial NHC track forecast is close to HCCA and a little south of the TVCA consensus, giving a little more weight to the GFS and ECMWF, which lie on the south side of the track guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT  22/1500Z  8.3N  23.6W   35 KT  40 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 12H  23/0000Z  8.8N  25.7W   40 KT  45 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 24H  23/1200Z  9.3N  29.6W   45 KT  50 MPH - Tropical Storm (WSW São Filipe, Cape Verde)
 36H  24/0000Z  9.4N  34.0W   50 KT  60 MPH - Tropical Storm (ESE Bridgetown, Barbados)
 48H  24/1200Z  9.6N  38.6W   50 KT  60 MPH - Tropical Storm (ESE Bridgetown, Barbados)
 72H  25/1200Z 10.3N  46.8W   50 KT  60 MPH - Tropical Storm (ESE Bridgetown, Barbados)
 96H  26/1200Z 11.0N  53.0W   50 KT  60 MPH - Tropical Storm (ESE Bridgetown, Barbados)
120H  27/1200Z 12.5N  58.5W   45 KT  50 MPH - Tropical Storm (ESE Bridgetown, Barbados)

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