headline - dtn · 2017. 7. 6. · prepared by wdt weatherops forecaster: lawson | 405.801.3919 |...

Effective: July 06, 2017 – 0400 CT / 0900 UTC

Invest 94L developed into Tropical Depression Four; slight strengthening possible but not expected the next 24 hours.

General Discussion

A trough over the Central Atlantic is generating moderate to strong wind shear just to the northeast of the Lesser Antilles. Despite warm sea-surface temperatures and pockets of lesser shear, notable dry Saharan air is noted via latest satellite imagery. As such, the environment across the North Atlantic Basin is only marginally conducive for tropical development. Further east, Invest 94L, previously an area of low pressure with associated shower and thunderstorm activity, has developed a low-level circulation as well as enhanced convection, and is now Tropical Depression Four. This system is not expected to experience significant organization over the next few days due to the previously mentioned dry air, but some strengthening cannot be ruled out over the next 24 hours. Elsewhere, tropical cyclone development chances will remain low.

Active Tropical Threats

Feature # Name Current Location

5-Day Development Potential

Sustained Wind

Current Movement

04L Tropical Depression Four 13.2N 40.0W 50% 25 knots WNW at 15 knots

Atlantic Tropical Daily Planner

HEADLINE

Prepared by WDT WeatherOps Forecaster: LAWSON | 405.801.3919 | WDTinc.com

Strong Wind Shear

Strong Wind ShearTD Four

Dry Air

Dry Air



Environmental Favorability for Tropical Cyclones

Current SST’s Tropical Cyclone Heat Potential

Current Wind Shear Current Mid-Level Dry Air

ECMWF Surface Winds Valid at 0900 UTC July 06 2017

Tropical Depression Four

Position and Intensity Threat Briefing

Feature Center: 13.2N 40.0W Dry Saharan air to the west of Tropical Depression Four is expected to limit significant further development and Four is forecast to remain just below tropical storm strength. Regardless, strong to gale force winds and moderate to rough seas, along with showers and thunderstorms may accompany Four’s passage. Four is expected to track to the west-northwest with an extra-tropical transition and gradual weakening. Minimal impacts are forecast across the Lesser Antilles by day three and four.

Current Movement: WNW at 15 knots

Current Sustained Winds: 25 knots

Current Wind Gusts: 35 knots

Infrared Satellite Image of TD Four5 Day Development Potential

TD 100%

TS 50%

CAT 1 10%

CAT 2 0%

CAT 3 0%

CAT 4 0%

CAT 5 0%



Saffir-Simpson Scale Reference

Intensity Wind Speed (KTS)

TD 25 - 33

TS 34 - 63

CAT 1 64 - 82

CAT 2 83 - 95

CAT 3 96 - 112

CAT 4 113 - 136

CAT 5 137 +

Tropical Depression Four Advisory #2 Effective: July 6, 2017 0900 UTC (06/0400 CT)

Storm Center 13.2N 40.0W (about 1246 nm E of the Lesser Antilles)

Current Movement WNW at 15 knots

Sustained Winds/Gusts 25 knots / 35 knots

34 kt Wind Radii 0 NE 0 SE 0 SW 0 NW



Forecast Trend Tropical Depression Four has not changed much over the last several hours and has continued to track west-northwestward.

Prepared by WDT WeatherOps Forecaster: FUCHECK | 405.801.3919 | WDTinc.com

WDT FORECAST TRACK

Active Storm Advisory

WIND RADII 34kt+ 50kt+ 64kt+

WDT Forecast Positions and Max WindsTrack Forecast Confidence: Average Intensity Forecast Confidence: Average

Date Forecast Time/Hour Position Sustained Winds Saffir-Simpson ScaleThu July 6 0900 UTC Initial 13.2N 40.0W 25 KT 30 MPH TDThu July 6 1800 UTC 12 Hour 14.1N 43.0W 30 KT 35 MPH TD Fri July 7 0600 UTC 24 Hour 15.0N 46.2W 30 KT 35 MPH TD Fri July 7 1800 UTC 36 Hour 16.3N 50.0W 30 KT 35 MPH TD Sat July 8 0600 UTC 48 Hour 17.5N 53.5W 25 KT 30 MPH TD (DISSIPATING)Sun July 9 0600 UTC 72 Hour 20.5N 59.5W 25 KT 30 MPH REMNANT LOWMon July 10 0600 UTC 96 Hour 23.0N 65.0W 25 KT 25 MPH REMNANT LOW

- - - - - - - -

Initial

24 HR

48 HR

72 HR

96 HR

WDT Forecast Discussion

Observational Perspective: Not much has changed since the previous update. Deep convection continues to form around TD Fours low level circulation with favorable upper level outflow currently overspreading much of the system. Given the storms current structure and most recent satellite derived winds, Tropical Depression Four’s intensity remains at 25 knots.

Intensity Forecast: Not much has changed since the previous update. Currently the system is in a somewhat favorable environment for further development with low wind shear and warm sea surface temperatures, but Saharan dry air is currently beginning to enter the northern periphery of the systems circulation. Given this, some slight additional strengthening is forecast over the next day or so. Afterward, dry air entrainment and increasing wind shear are forecast to weaken the system into a remnant low by day 3 or 4.

Track Forecast: No changes since the previous forecast. With a ridge to the north of TD Four, the system will continue to track west-northwestwards along the southern periphery of this ridge over the next few days. Then as the system gets to the western periphery of this ridge in the western Atlantic, TD Four is then forecast to begin to reduce its current forward motion and begin tracking to the northwest as a remnant low.

WDT’s next advisory will be issued at 1500 UTC / 1000 CT

Tropical Depression Four Advisory #2 Effective: July 6, 2017 0900 UTC (06/0400 CT)

Changes from Previous Advisory

No significant changes since the previous advisory.

Marine Weather Impacts

Strong to near gale force winds with gale force gusts currently extend out about 60 nm from the center of TD Four on the northern and western periphery of its circulation. These winds are currently not forecast to change much over the next few days. Moderate to near rough seas currently extend out 120 nm from the center of TD Four with rough seas forecast to form within the next 12 hours or so.

Onshore Impacts

At this time no onshore impacts are anticipated over the next five days.

Infrared Satellite Image

Active Storm Advisory

Prepared by WDT WeatherOps Forecaster: FUCHECK | 405.801.3919 | WDTinc.com

headline - dtn · 2017. 7. 6. · prepared by wdt weatherops forecaster: lawson | 405.801.3919 |...

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